Ultra-low temperature freezer, refrigeration system and vacuum apparatus

ABSTRACT

In an ultra-low temperature freezer (R) using refrigerant mixture in which plural kinds of refrigerants having different boiling points are mixed, in order to ensure the flow rate of liquid refrigerant into a supercooler ( 31 ) and enhance the cooling efficiency of a cryocoil ( 32 ), the ultra-low temperature freezer (R) comprises: a main refrigerant circuit ( 38 ) provided with the cryocoil ( 32 ) and a capillary tube ( 29 ); and a sub refrigerant circuit ( 39 ) that is connected at the upstream end to the upstream end of the main refrigerant circuit ( 38 ) to branch off therefrom and provided with a capillary tube ( 28 ), and the ultra-low temperature freezer (R) is configured so that the sub refrigerant circuit ( 39 ) is lower in height than the main refrigerant circuit ( 38 ). Thus, gas-liquid mixture refrigerant discharged from the primary side ( 31   a ) of the supercooler ( 31 ) flows into the sub refrigerant circuit ( 39 ) at a higher rate than into the main refrigerant circuit ( 38 ) and, in turn, liquid refrigerant flows more into the sub refrigerant circuit ( 39 ) than into the main refrigerant circuit ( 38 ).

TECHNICAL FIELD

This invention relates to an ultra-low temperature freezer for creating a cold environment at an ultra-low temperature level, a refrigeration system for the same purpose and a vacuum apparatus provided with one of them.

BACKGROUND ART

Conventionally known refrigeration systems for creating a cold environment at an ultra-low temperature level of −100° C. or below include mixed refrigerant type ultra-low temperature freezers in which a refrigerant circuit is charged with a non-azeotropic refrigerant mixture obtained by mixing plural kinds of refrigerants having different boiling temperatures, as disclosed, for example, in Patent Documents 1, 2 and 3. An ultra-low temperature freezer of such kind is placed in, for example, a vacuum chamber of a vacuum deposition apparatus for use in manufacturing substrates (wafers), and used to raise the vacuum level in the vacuum chamber by trapping moisture or the like in it by freezing.

The refrigerant circuit of the above refrigeration system includes, as fundamental components, for example, a compressor, a condenser, multiple stages of gas-liquid separators, multiple stages of cascade heat exchangers, a plurality of pressure reducing elements and a cooler (evaporator). Out of the refrigerant mixture discharged from the compressor, mainly a high-boiling refrigerant component is condensed by the condenser, the condensed refrigerant is separated into liquid and gas refrigerants by the first-stage gas-liquid separator, the gas refrigerant is then cooled in the primary side of the first-stage cascade heat exchanger by heat exchange with the liquid refrigerant separated as above and then reduced in pressure. Further, heat exchange takes place likewise also in the second-stage and subsequent cascade heat exchangers. Specifically, in the cascade heat exchanger of each stage, refrigerant condensed by the cascade heat exchanger of the preceding stage is separated into gas and liquid refrigerants. The separated liquid refrigerant is reduced in pressure by the corresponding pressure reducing element and then evaporated by the corresponding heat exchanger of the same stage. The heat of evaporation thus obtained is used to cool the gas refrigerant coming from the gas-liquid separator to condense it. In this manner, the multiple stages of cascade heat exchangers individually condense the refrigerant mixture components in order from a highest-boiling refrigerant component to a lowest-boiling refrigerant component. The liquid refrigerant having flowed out of the primary side of the final-stage cascade heat exchanger is reduced in pressure by the pressure reducing element such as a capillary tube and then evaporated in the cooler. Thus, a cold environment at an ultra-low temperature level of −100° C. or below is created and the cold environment in the cooler is used to cool an cooling target to trap, for example, moisture or the like in the vacuum chamber. Further, the gas refrigerant obtained as the result of the liquid refrigerant having a cooling effect in the cooler to thereby evaporate is returned to the secondary side of the final-stage cascade heat exchanger and then returned through the secondary sides of the cascade heat exchangers of the preceding stages to the compressor.

Furthermore, a sub refrigerant circuit branches off from and is connected in parallel with the main refrigerant circuit including the pressure reducing element and the cooler. The sub refrigerant circuit is provided with a pressure reducing element for a supercooler. Between the condenser and the cooler, the supercooler is disposed which is formed of a heat exchanger having a primary side through which flows the refrigerant discharged from the condenser and a secondary side through which flows the refrigerant heat-exchangeable with the refrigerant in the primary side. The supercooler cools the refrigerant in the primary side by heat exchange with the refrigerant in the secondary side. The pressure reducing element for the supercooler is for reducing the pressure of the liquid refrigerant that will be supplied to the secondary side of the supercooler for the purpose of heat exchange.

Furthermore, a refrigerator oil for preventing sticking of a sliding bearing or the like in the compressor is mixed into the refrigerant mixture. An oil separator for removing the refrigerator oil from the refrigerant mixture is disposed between the discharge side of the compressor and the condenser. This prevents that the refrigerator oil is supplied to the cooler and solidifies to deteriorate the cooling efficiency.

Furthermore, at the start of operation of such a mixed refrigerant type ultra-low temperature freezer, the low-boiling refrigerant component may not sufficiently condense and, therefore, the discharge pressure may increase and might even exceed the withstanding pressure of the freezer. To cope with this, the freezer is additionally provided with a buffer tank and the buffer tank is connected to the refrigerant circuit via a pipe with a valve that operates when the pressure in the refrigerant circuit exceeds a predetermined pressure (for example, a pressure slightly lower than the design withstanding pressure). Thus, high-pressure refrigerant is temporarily released into the buffer tank and the discharge pressure is reduced to make the freezer operable.

In a freezer shown in Patent Document 4, the buffer tank is connected to the suction side of the compressor via a return pipe so that refrigerant in the buffer tank can be circulated into the refrigerant circuit.

Furthermore, since the above vacuum deposition apparatus traps moisture by the cooler (main cooler), it is necessary that when film deposition is not carried out, the normal operation of the freezer is halted and the cooler is defrosted. Therefore, in the ultra-low temperature freezers, the discharge side of the compressor is connected to the cooler through a defrosting circuit and a defrosting operation is performed to supply the discharge gas from the compressor to the cooler and thereby defrost the cooler.

Patent Document 1: Published Registered Japanese Utility Model No. 2559220

Patent Document 2: Published Unexamined Japanese Patent Application No. H02-67855 Patent Document 3: Published Unexamined Japanese Patent Application No. H06-347112 Patent Document 4: Published Unexamined Japanese Patent Application No. H06-159831

DISCLOSURE OF THE INVENTION Problems to Be Solved by the Invention

The above conventional refrigeration systems, however, have problems described below.

(1) First, the refrigeration system with the supercooler connected as described above is normally configured so that refrigerant flowing through the main cooler is equal in flow rate to refrigerant flowing through the secondary side of the supercooler.

However, the refrigerant passing through the bifurcation of the main and sub refrigerant circuits into the main cooler and the secondary side of the supercooler is not fully composed of liquid refrigerant but is supplied to both the coolers as gas-liquid mixture refrigerant partly containing gas refrigerant. Therefore, even if the system is configured so that refrigerant flowing through the main cooler is equal in flow rate to refrigerant flowing through the supercooler, if the flow rate of liquid refrigerant into the secondary side of the supercooler is low, this provides a shortage of cooling of gas refrigerant in the primary side thereof. The flow rate of liquid refrigerant obtained by gas refrigerant liquefaction of the supercooler is correspondingly reduced, which invites deteriorated cooling efficiency of the main cooler. As a result, in the case of load variations of the cooling target to be cooled by the main cooler, there arises a problem of impossibility to stably cool the cooling target against such load variations or a problem of extended cool-down time taken for the main cooler to cool down the cooling target from normal to ultra-low temperature level.

(2) Further, when the normal operation of the freezer is halted and a defrosting operation is performed to supply the discharge gas from the compressor to the cooler through the defrosting circuit and thereby defrost the cooler, if refrigerator oil has failed to be completely removed by the oil separator and remains in it at the start of the defrosting operation, it may flow through the defrosting circuit and may be supplied to the cooler still at an ultra-low temperature level, which causes a problem that the refrigerator oil solidifies in the cooler.

(3) Furthermore, once the refrigerator oil or the like has been supplied to the cooler and has solidified in it, even if the refrigerator oil can then pass through the cooler owing to later temperature increase of the cooler, the refrigerator oil or the like going out of the cooler is supplied to the heat exchanger at a similar ultra-low temperature level. Therefore, the refrigerator oil or the like solidifies also in the heat exchanger. This causes a problem that it takes a long time to eliminate solidification of the refrigerator oil or the like and the defrosting operation time is thereby extended.

To solve the problem of solidification of the refrigerator oil or the like in the cooler, it can be considered to arrange a plurality of oil separators in series between the discharge side of the compressor and the condenser. This method, however, causes pressure loss due to flow resistance of the refrigerant mixture and invites another problem that the cooling efficiency deteriorates.

(4) Furthermore, low-boiling refrigerants remaining in the gas phase even in operation and halt of a freezer have come into increasing use in recent years in order to enhance the cooling capacity of the freezer. Therefore, there arises a problem of shortage of capacity of the buffer tank.

To eliminate such a shortage of capacity of the buffer tank, it is possible to use a large-capacity buffer tank. In the case of simply increasing the tank volume, however, it is difficult to obtain an installation space for the tank. Further, since refrigerants of different boiling points have different specific gravities, some of the refrigerant components may be difficult to fully circulate through the refrigerant circuit depending upon the connecting point of the refrigerant return pipe for returning the refrigerant from the tank to the refrigerant circuit. Therefore, the composition of the refrigerant mixture may vary depending on different parts of the freezer and from that of the refrigerant mixture just after charged in the refrigerant circuit, which may provide deteriorated cooling capacity.

(5) Furthermore, in the above ultra-low temperature freezers, if the cooler can be cooled from normal to ultra-low temperature level in a short time, this is desirable, for example, because the operating efficiency of the vacuum apparatus is improved. If a capillary tube is used as the pressure reducing element and the total length of the capillary tube is shortened to reduce the flow resistance, the cooler can be cooled to a low-temperature level in a short time, which makes it possible to satisfy the above demand. On the other hand, however, this makes it difficult to cool the cooler down to a predetermined cooling temperature.

On the contrary, if the total length of the capillary tube is elongated to increase the flow resistance, refrigerant can be reduced down to a pressure at which the evaporation temperature of the low-boiling refrigerant can be sufficiently lowered to cool the cooling target down to an ultra-low temperature level. On the other hand, however, the flow rate of refrigerant becomes low, which makes it difficult to quickly cool the cooling target in a short time.

As can be seen from the above, with the conventional circuit configurations for pressure reducing elements, it is difficult to cool the cooler down to an ultra-low temperature level in a short time.

The present invention has been made with the foregoing points in mind and a first object of the invention is to properly control the flow rate of refrigerant into the main cooler and the flow rate of refrigerant into the secondary side of the supercooler whereby the flow rate of liquid refrigerant into the supercooler is stably and sufficiently ensured to increase the cooling efficiency of the main cooler, stably cool the cooling target against load variations and shorten the cool-down time taken to cool down the cooling target from normal to ultra-low temperature level.

A second object of the present invention is that the ultra-low temperature freezer with a defrosting circuit as described above certainly removes the refrigerator oil without impairing its cooling efficiency to prevent the refrigerator oil from being supplied to the cooler.

A third object of the present invention is that the ultra-low temperature freezer with a defrosting circuit as described above restrains solidification of refrigerator oil or the like, particularly in a heat exchanger, to shorten the defrosting operation time.

A fourth object of the present invention is to provide a required large capacity of the buffer tank for the use of low-boiling refrigerants and effectively circulate gas refrigerant in the buffer tank into the refrigerant circuit.

A fifth object of the present invention is that the ultra-low temperature freezer can cool the cooler down to an ultra-low temperature level in a short time without impairing its cooling capacity.

Means for Solving the Problems

With the aim of achieving the above objects, a first aspect of the invention is intended to create a difference between the flow rates of liquid refrigerant into the main cooler and the supercooler and, to be specific, to make the flow rate of liquid refrigerant flowing into the secondary side of the supercooler higher than that of liquid refrigerant flowing into the main cooler.

More specifically, a refrigeration system of the first aspect of the invention is characterized by comprising: a compressor for compressing refrigerant; a condenser for cooling the refrigerant discharged from the compressor to condense the refrigerant; a supercooler, having a primary side through which the refrigerant discharged from the condenser flows and a secondary side through which the refrigerant discharged from the primary side and reduced in pressure by a supercooler pressure reducing element flows, for cooling the refrigerant in the primary side by heat exchange with the refrigerant in the secondary side; a main cooler for evaporating the refrigerant discharged from the primary side of the supercooler and reduced in pressure by a main cooler pressure reducing element to cool a cooling target; and a supercooler refrigerant flow rate increasing device for allowing liquid refrigerant of the refrigerant discharged from the primary side of the supercooler to flow into the secondary side of the supercooler at a higher rate than into the main cooler.

A refrigeration system of a second aspect of the invention is characterized by comprising: a compressor for compressing refrigerant mixture in which plural kinds of refrigerants having different boiling points are mixed; a condenser for cooling a high-boiling refrigerant component in the refrigerant mixture discharged from the compressor to condense the high-boiling refrigerant component; multiple stages of gas-liquid separators for separating individual refrigerant components in the refrigerant mixture discharged from the condenser into liquid refrigerant and gas refrigerant in order from higher- to lower-boiling refrigerant components; multiple stages of cascade heat exchangers for individually cooling the gas refrigerant separated by the associated gas-liquid separator by heat exchange with the liquid refrigerant separated by the associated gas-liquid separator and then reduced in pressure by a pressure reducing element; a supercooler, having a primary side through which the low-boiling refrigerant component discharged from the final-stage cascade heat exchanger flows and a secondary side through which the low-boiling refrigerant component discharged from the primary side and reduced in pressure by a supercooler pressure reducing element flows, for cooling the low-boiling refrigerant component in the primary side by heat exchange with the low-boiling refrigerant component in the secondary side; a main cooler for evaporating the low-boiling refrigerant component discharged from the primary side of the supercooler and reduced in pressure by a main cooler pressure reducing element to cool a cooling target down to an ultra-low temperature level; and a supercooler refrigerant flow rate increasing device for allowing liquid refrigerant of the refrigerant discharged from the primary side of the supercooler to flow into the secondary side of the supercooler at a higher rate than into the main cooler.

Since in the configurations of the above aspects the flow rate of liquid refrigerant flowing into the secondary side of the supercooler is higher than that of liquid refrigerant into the main cooler, this ensures sufficient cooing of gas refrigerant in the primary side of the supercooler, which increases the flow rate of liquid refrigerant obtained by the gas refrigerant liquefaction of the supercooler and thereby enhances the cooling efficiency of the main cooler. Accordingly, even in the case of load variations of a cooling target to be cooled by the main cooler, the cooling target can be stably cooled and can be quickly cooled down from normal to ultra-low temperature level to shorten the cool-down time.

A third aspect of the invention is characterized in that the refrigeration system further comprises: a main refrigerant circuit provided with the main cooler and the main cooler pressure reducing element; and a sub refrigerant circuit that is connected at the upstream end to the upstream end of the main refrigerant circuit to branch off therefrom and provided with the supercooler pressure reducing element, and the supercooler refrigerant flow rate increasing device is configured so that the minimum cross sectional area of the sub refrigerant circuit is larger than the maximum cross sectional area of the main refrigerant circuit.

Since in this case the minimum cross sectional area of the sub refrigerant circuit is larger than the maximum cross sectional area of the main refrigerant circuit, when the refrigerant discharged from the primary side of the supercooler is distributed into the main and sub refrigerant circuits, the flow rate of the gas-liquid mixture refrigerant into the sub refrigerant circuit, taken as a whole, becomes higher than that of the gas-liquid mixture refrigerant into the main refrigerant circuit. Therefore, the flow rate of liquid refrigerant into the sub refrigerant circuit becomes proportionately higher than that of liquid refrigerant into the main refrigerant circuit. This provides sufficient cooling of gas refrigerant in the primary side of the supercooler, which increases the flow rate of liquid refrigerant obtained by the gas refrigerant liquefaction of the supercooler and thereby enhances the cooling efficiency of the main cooler.

A fourth aspect of the invention is characterized in that the refrigeration system further comprises: a main refrigerant circuit provided with the main cooler and the main cooler pressure reducing element; and a sub refrigerant circuit that is connected at the upstream end to the upstream end of the main refrigerant circuit to branch off therefrom and provided with the supercooler pressure reducing element, and the supercooler refrigerant flow rate increasing device is configured so that the maximum height of the sub refrigerant circuit at the bifurcation of the main and sub refrigerant circuits is lower than the minimum height of the main refrigerant circuit at the bifurcation.

Since in this case the maximum height of the sub refrigerant circuit at the bifurcation of the main and sub refrigerant circuits is lower than the minimum height of the main refrigerant circuit at the bifurcation, when the refrigerant discharged from the primary side of the supercooler is distributed into the main and sub refrigerant circuits, liquid refrigerant of the gas-liquid mixture refrigerant flows more into the sub refrigerant circuit of relatively small height. Therefore, the flow rate of liquid refrigerant into the sub refrigerant circuit becomes higher than that of liquid refrigerant into the main refrigerant circuit. This ensures sufficient cooling of gas refrigerant in the primary side of the supercooler, which increases the flow rate of liquid refrigerant obtained by the gas refrigerant liquefaction of the supercooler and thereby enhances the cooling efficiency of the main cooler.

In addition, the supercooler refrigerant flow rate increasing device is implemented simply by creating a difference in height between the main and sub refrigerant circuits and does not need to be formed with passages having different cross sectional areas. Therefore, the above effects can be obtained with a simple structure.

A fifth aspect of the invention is characterized, in the refrigeration system of the third aspect of the invention, in that the supercooler refrigerant flow rate increasing device is configured so that the maximum height of the sub refrigerant circuit at the bifurcation of the main and sub refrigerant circuits is lower than the minimum height of the main refrigerant circuit at the bifurcation. Thus, the behaviors and effects of the third and fourth aspects can synergistically act to further enhance the cooling efficiency of the main cooler.

A sixth aspect of the invention is characterized by a vacuum apparatus configured to freeze moisture in a vacuum chamber by cooling the moisture through the main cooler in the refrigeration system of any one of the first to fifth aspects of the invention. Thus, moisture in the vacuum chamber of the vacuum apparatus can be frozen, which provides a stable vacuum condition in the vacuum chamber and shortened cool-down time. The shortened cool-down time enables a short-time exhaust of the vacuum chamber and in turn enhances production efficiency.

A seventh aspect of the invention is intended to remove refrigerator oil from refrigerant mixture flowing into a defrosting circuit by disposing an oil separator for use in defrosting, not between the discharge side of the compressor and the condenser, but in the defrosting circuit.

Specifically, the seventh aspect of the invention is characterized by comprising: a compressor for compressing refrigerant mixture in which plural kinds of refrigerants having different boiling points are mixed; a condenser for cooling a high-boiling refrigerant component in the refrigerant mixture discharged from the compressor to liquefy the high-boiling refrigerant component; a first oil separator for removing, from the refrigerant mixture flowing from the discharge side of the compressor toward the condenser, refrigerator oil mixed in the refrigerant mixture; multiple stages of gas-liquid separators for separating individual refrigerant components in the refrigerant mixture liquefied by the condenser into liquid refrigerant and gas refrigerant in order from higher- to lower-boiling refrigerant components; multiple stages of cascade heat exchangers for individually cooling the gas refrigerant separated by the associated gas-liquid separator by heat exchange with the liquid refrigerant separated by the associated gas-liquid separator and reduced in pressure; a cooler for evaporating the low-boiling refrigerant component discharged from the final-stage cascade heat exchanger of the multiple stages of cascade heat exchangers and reduced in pressure to cool a cooling target down to an ultra-low temperature level; and a defrosting circuit for supplying the refrigerant mixture discharged from the compressor to the cooler during defrosting of the cooler, wherein the defrosting circuit is provided with a second oil separator for removing refrigerator oil from the refrigerant mixture.

Since in this aspect a second oil separator for removing refrigerator oil from the refrigerant mixture is disposed in the defrosting circuit, it can be prevented that, during defrosting, the refrigerator oil in the refrigerant mixture is supplied from the defrosting circuit to the cooler to solidify in the cooler.

Further, the above configuration prevents an increase in pressure loss that would be caused when a plurality of oil separators were disposed in series between the discharge side of the compressor and the condenser. This provides an effect of preventing the above-described deterioration of the cooling efficiency while circulating the refrigerant mixture well.

Furthermore, since the second oil separator is disposed in the defrosting circuit, parts can be standardized with freezers having no defrosting circuit, which is advantageous in reducing equipment cost. Furthermore, maintenance work such as replacement can be easily carried out.

An eighth aspect of the invention is characterized in that the defrosting circuit is provided with a shut-off valve that is opened during defrosting, and the second oil separator is disposed between the upstream end of the defrosting circuit and the shut-off valve.

Since in this aspect the second oil separator is disposed between the upstream end of the defrosting circuit and the shut-off valve, the closing of the shut-off valve prevents that a pressure difference occurs between the suction side of the compressor and the second oil separator, with the former having a higher pressure than the latter.

Specifically, the second oil separator and the compressor are connected to return the separated refrigerator oil to the suction side of the compressor. Therefore, if a pressure difference occurs between the suction side of the compressor and the second oil separator so that the former has a higher pressure than the latter, the refrigerator oil might flow from the compressor back to the second oil separator. When the shut-off valve disposed downstream of the second oil separator is closed, however, this prevents the occurrence of a pressure difference as described above and prevents backflow of refrigerator oil to smoothly return the refrigerator oil to the compressor.

A ninth aspect is characterized in that the second oil separator is disposed at a location along the defrosting circuit at which the distance to the upstream end of the defrosting circuit is shorter than the distance to the downstream end thereof.

Since in this aspect the second oil separator is disposed at a location along the defrosting circuit at which the distance to the upstream end of the defrosting circuit is shorter than the distance to the downstream end thereof, even high-temperature and low-viscosity refrigerator oil can be separated, which enables the removal of refrigerator oil with higher reliability.

In a tenth aspect of the invention, a plurality of buffer tanks are provided in an ultra-low temperature freezer and connected to each other via pipes. Thus, gas refrigerant can be smoothly circulated from one tank to another and the retention of gas refrigerant in the tanks can be prevented to efficiently circulate the gas refrigerant.

Specifically, an ultra-low temperature freezer of the tenth aspect of the invention comprises a refrigerant circuit in which are connected: a compressor for compressing refrigerant mixture in which plural kinds of refrigerants having different boiling points are mixed; a condenser for cooling a high-boiling refrigerant component in the refrigerant mixture discharged from the compressor to liquefy the high-boiling refrigerant component; multiple stages of gas-liquid separators for separating individual refrigerant components in the refrigerant mixture liquefied by the condenser into liquid refrigerant and gas refrigerant in order from higher- to lower-boiling refrigerant components; multiple stages of cascade heat exchangers for individually cooling the gas refrigerant separated by the associated gas-liquid separator by heat exchange with the liquid refrigerant separated by the associated gas-liquid separator and reduced in pressure; and a cooler for evaporating the low-boiling refrigerant component discharged from the final-stage cascade heat exchanger of the multiple stages of cascade heat exchangers and reduced in pressure to cool a cooling target down to an ultra-low temperature level.

Further, the ultra-low temperature freezer is characterized in that the refrigerant circuit is connected with a plurality of buffer tanks for restraining abnormal increase in the discharge pressure of the compressor.

Since in this aspect a plurality of buffer tanks are connected to the refrigerant circuit, the tank installation space can be easily saved in a factory or the like as compared with where a single large-capacity tank is connected to the refrigerant circuit in order to eliminate shortage of tank capacity. Further, since the plurality of buffer tanks increase the total tank capacity, this prevents abnormal increase in the discharge pressure of the compressor, which is advantageous for stable operation of the freezer.

An eleventh aspect of the invention is characterized, in the ultra-low temperature freezer of the tenth aspect, in that the plurality of buffer tanks include at least one first buffer tank and at least one second buffer tank located below the first buffer tank, the first and second buffer tanks are connected to each other through a communicating passage for providing flow communication of gas refrigerant between the first and second buffer tanks, and the second buffer tank is connected to one side of the refrigerant circuit toward the discharge part of the compressor and the other side toward the suction part of the compressor.

Since in this aspect the first and second buffer tanks are connected to each other through a communicating passage, refrigerant can be moved between both the tanks. Thus, the retention of gas refrigerant in the tanks can be prevented to provide circulation of all the refrigerant components of different specific gravities throughout the refrigerant circuit. This prevents that the refrigerant mixture moving in the freezer varies in composition from that just after charged into the refrigerant circuit to deteriorate the cooling capacity.

A twelfth aspect of the invention is characterized, in the ultra-low temperature freezer of the tenth aspect, in that the plurality of buffer tanks include at least one first buffer tank and at least one second buffer tank, the first and second buffer tanks are connected to each other through a communicating passage for providing flow communication of gas refrigerant between the first and second buffer tanks, the first buffer tank is connected to the side of the refrigerant circuit located toward the discharge part of the compressor, and the communicating passage is connected partway therethrough to the side of the refrigerant circuit located toward the suction part of the compressor.

Since in this aspect the first and second buffer tanks are connected to each other through a communicating passage, refrigerant can be moved between both the tanks. Thus, the retention of gas refrigerant in the tanks can be prevented to provide circulation of all the refrigerant components of different specific gravities throughout the refrigerant circuit. This prevents that the refrigerant mixture moving in the freezer varies in composition from that just after charged into the refrigerant circuit to deteriorate the cooling capacity.

Further, since the communicating passage is connected partway therethrough to the side of the refrigerant circuit located toward the suction part of the compressor, in the course of gas refrigerant flowing from the refrigerant circuit into the buffer tank and returning to the suction side of the compressor, the gas refrigerant smoothly circulates in both the buffer tanks. Thus, the retention of gas refrigerant in the tank can be prevented with higher reliability.

A thirteenth aspect of the invention is characterized, in the ultra-low temperature freezer of the tenth aspect, in that the plurality of buffer tanks include at least one first buffer tank and at least one second buffer tank, the first and second buffer tanks are connected to each other through a communicating passage for providing flow communication of gas refrigerant between the first and second buffer tanks, the first buffer tank is connected to the side of the refrigerant circuit located toward the discharge part of the compressor, and the second buffer tank is connected to the side of the refrigerant circuit located toward the suction part of the compressor.

Since in this aspect the first and second buffer tanks are connected to each other through a communicating passage, refrigerant can be moved between both the tanks. Thus, the retention of gas refrigerant in the tanks can be prevented to provide circulation of all the refrigerant components of different specific gravities throughout the refrigerant circuit. This prevents that the refrigerant mixture moving in the freezer varies in composition from that just after charged into the refrigerant circuit to deteriorate the cooling capacity.

Further, the above circuit configuration prevents the retention of gas refrigerant in the tanks with higher reliability.

A fourteenth aspect of the invention is intended to allow concurrent temperature increase of the cooler and one of the heat exchangers by dividing the downstream end part of the defrosting circuit into two branches.

Specifically, the fourteenth aspect of the invention is directed to an ultra-low temperature freezer comprising a refrigerant circuit in which are connected: a compressor for compressing refrigerant mixture in which plural kinds of refrigerants having different boiling points are mixed; a condenser for cooling a high-boiling refrigerant component in the refrigerant mixture discharged from the compressor to liquefy the high-boiling refrigerant component; multiple stages of gas-liquid separators for separating individual refrigerant components in the refrigerant mixture liquefied by the condenser into liquid refrigerant and gas refrigerant in order from higher- to lower-boiling refrigerant components; multiple stages of cascade heat exchangers for individually cooling the gas refrigerant separated by the associated gas-liquid separator by heat exchange with the liquid refrigerant separated by the associated gas-liquid separator and reduced in pressure; and a cooler for evaporating the low-boiling refrigerant component discharged from the final-stage cascade heat exchanger of the multiple stages of cascade heat exchangers and reduced in pressure to cool a cooling target down to an ultra-low temperature level, and a defrosting circuit for supplying the refrigerant mixture discharged from the compressor to the cooler during defrosting of the cooler.

Further, the fourteenth aspect of the invention is characterized in that the downstream end part of the defrosting circuit is branched into a main branch circuit and a sub-branch circuit, the downstream end of the main branch circuit is connected to one side of the refrigerant circuit toward the entrance of the cooler, and the downstream end of the sub-branch circuit is connected to the other side of the refrigerant circuit toward the exit of the cooler.

In this aspect, out of the main and sub-branch circuits into which the downstream end part of the defrosting circuit is divided, the main branch circuit is connected at the downstream end to one side of the refrigerant circuit toward the entrance of the cooler and the sub-branch circuit is connected at the downstream end to the other side of the refrigerant circuit toward the exit of the cooler. Therefore, the refrigerant flowing through the main branch circuit can be supplied to the cooler to raise the temperature of the cooler and, concurrently, the refrigerant flowing through the sub-branch circuit can be supplied to the heat exchangers connected to the side of the refrigerant circuit toward the exit of the cooler to raise the temperature of the heat exchangers. Thus, refrigerator oil or the like having passed through the cooler can be prevented from solidifying again in the heat exchanger. Because it can be prevented that the refrigerant circuit is occluded owing to the solidification of the refrigerator oil or the like, this ensures good circulation of the refrigerant mixture in the refrigerant circuit, thereby shortening the defrosting operation time.

A fifteenth aspect of the invention is characterized in that the sub-branch circuit in the ultra-low temperature freezer of the fourteenth aspect is provided with a shut-off valve.

In this aspect, the shut-off valve is opened to raise the temperatures of the cooler and the heat exchanger as described above and then closed after refrigerator oil or the like in the heat exchanger is heated to or above the pour point at which it can flow smoothly. Thus, the refrigerant mixture having been distributed into the main and sub-branch circuits can be sent only to the main branch circuit to raise the temperature of the cooler, which further shortens the defrosting operation time.

In a sixteenth aspect of the invention, part of the refrigerant circuit toward the cooler is divided into a plurality of branch circuits connected in parallel with each other and branch pressure reducing elements are connected into the branch circuits, respectively, so that the refrigerant can flow selectively through the plurality of branch pressure reducing elements.

Specifically, the sixteenth aspect of the invention is directed to an ultra-low temperature freezer comprising a refrigerant circuit in which are connected: a compressor for compressing refrigerant mixture in which plural kinds of refrigerants having different boiling points are mixed; a condenser for cooling a high-boiling refrigerant component in the refrigerant mixture discharged from the compressor to liquefy the high-boiling refrigerant component; multiple stages of gas-liquid separators for separating individual refrigerant components in the refrigerant mixture liquefied by the condenser into liquid refrigerant and gas refrigerant in order from higher- to lower-boiling refrigerant components; multiple stages of cascade heat exchangers for individually cooling the gas refrigerant separated by the associated gas-liquid separator by heat exchange with the liquid refrigerant separated by the associated gas-liquid separator and reduced in pressure; a pressure reducing element for reducing the pressure of the low-boiling refrigerant component discharged from the final-stage cascade heat exchanger of the multiple stages of cascade heat exchangers; and a cooler for evaporating the low-boiling refrigerant component reduced in pressure by the pressure reducing element to cool a cooling target down to an ultra-low temperature level.

Further, the sixteenth aspect of the invention is characterized in that part of the refrigerant circuit for supplying refrigerant from the final-stage cascade heat exchanger to the cooler comprises a plurality of branch circuits connected in parallel with each other, the pressure reducing element comprises a plurality of branch pressure reducing elements series-connected into the plurality of branch circuits, respectively, and at least one of the plurality of branch circuits is provided with a selector for turning the at least one branch circuit on to pass the refrigerant therethrough.

Since in this aspect branch pressure reducing elements are connected into a plurality of parallel-connected branch circuits, respectively, and at least one of the plurality of branch circuits is provided with a selector for turning the at least one branch circuit on to pass the refrigerant therethrough, the refrigerant can be distributed into the plurality of branch circuits by the operation of the selector to increase the flow rate. This shortens the cooling time taken until the cooling target reaches a predetermined cooling temperature while ensuring a required pressure reduction capability to cool the cooling target down to the predetermined cooling temperature by changing the flow resistance of refrigerant.

A seventeenth aspect of the invention is characterized, in the ultra-low temperature freezer of the sixteenth aspect, in that the selector comprises a shut-off valve disposed in at least one of the plurality of branch circuits.

According to this aspect, the one or more shut-off valves are selectively opened, so that the flow rate of refrigerant to be distributed into the plurality of branch circuits can be controlled. This enables flexible control on the cooling temperature and cooling time of the cooler.

An eighteenth aspect of the invention is characterized, in the ultra-low temperature freezer of the sixteenth or seventeenth aspect, in that the plurality of branch pressure reducing elements have different pressure reduction capabilities.

Since in this aspect the plurality of branch pressure reducing elements have different pressure reduction capabilities, the control ranges of the cooling temperature and cooling time of the cooler can be widened as compared with where the plurality of branch pressure reducing elements have the same pressure reduction capability.

A nineteenth aspect of the invention is characterized, in the ultra-low temperature freezer of any one of the sixteenth to eighteenth aspects, in that the branch pressure reducing element comprises a capillary tube.

Since in this aspect a capillary tube is used as the branch pressure reducing element, the low-boiling refrigerant component can be reliably reduced in pressure even in an ultra-low temperature range. The use of the capillary tube is higher in reliability than the use of an expansion valve or the like as the pressure reducing element, which is advantageous for stable operation of the freezer. Further, since capillary tubes are lower in price than expansion valves, the equipment cost can be significantly reduced.

Further, a twentieth aspect of the invention is characterized by a vacuum apparatus configured to freeze moisture in a vacuum chamber by cooling the moisture with the cooler in the ultra-low temperature freezer of any one of the seventh to nineteenth aspects. This enhances the production efficiency and operational stability of the vacuum apparatus.

Effects of the Invention

As described so far, the first or second aspect of the invention is directed to a refrigeration system comprising a main cooler for cooling a cooling target and a supercooler for cooling refrigerant in its primary side with refrigerant in its secondary side, wherein the refrigeration system further comprises a supercooler refrigerant flow rate increasing device for allowing liquid refrigerant to flow into the secondary side of the supercooler at a higher rate than into the main cooler. Therefore, sufficient cooling of gas refrigerant in the primary side of the supercooler can be ensured to enhance the cooling efficiency of the main cooler. This provides stable cooling of the cooling target and shortens the cool-down time taken to cool the cooling target down to an ultra-low temperature level.

In the third aspect of the invention, the refrigeration system further comprises: a main refrigerant circuit provided with the main cooler and the main cooler pressure reducing element; and a sub refrigerant circuit that is connected to the main refrigerant circuit to branch off therefrom and provided with the supercooler pressure reducing element, and the supercooler refrigerant flow rate increasing device is configured so that the minimum cross sectional area of the sub refrigerant circuit is larger than the maximum cross sectional area of the main refrigerant circuit. Thus, when the refrigerant discharged from the primary side of the supercooler is distributed into the main and sub refrigerant circuits, gas-liquid mixture refrigerant can flow into the sub refrigerant circuit at a higher rate than into the main refrigerant circuit, and, in turn, liquid refrigerant can flow into the sub refrigerant circuit at a higher rate than into the main refrigerant circuit. In this manner, the supercooler refrigerant flow rate increasing device can be achieved.

In the fourth aspect of the invention, the refrigeration system further comprises: a main refrigerant circuit provided with the main cooler and the main cooler pressure reducing element; and a sub refrigerant circuit that is connected to the main refrigerant circuit to branch off therefrom and provided with the supercooler pressure reducing element, and the supercooler refrigerant flow rate increasing device is configured so that the maximum height of the sub refrigerant circuit at the bifurcation of the main and sub refrigerant circuits is lower than the minimum height of the main refrigerant circuit at the bifurcation. Thus, when the refrigerant discharged from the primary side of the supercooler is distributed into the main and sub refrigerant circuits, liquid refrigerant of the gas-liquid mixture refrigerant can flow into the sub refrigerant circuit of relatively small height, and, in turn, liquid refrigerant can flow into the sub refrigerant circuit at a higher rate than into the main refrigerant circuit. Therefore, the supercooler refrigerant flow rate increasing device can be achieved with a simple structure.

According to the fifth aspect of the invention, since in the refrigeration system of the third aspect the maximum height of the sub refrigerant circuit at the bifurcation of the main and sub refrigerant circuits is lower than the minimum height of the main refrigerant circuit at the bifurcation, the behaviors and effects of the third and fourth aspects can synergistically act to further enhance the cooling efficiency of the main cooler.

According to the sixth aspect of the invention, since moisture in a vacuum chamber of a vacuum apparatus is frozen by cooling it using the main cooler of the refrigeration system, this provides a stable vacuum condition in the vacuum chamber and shortened cool-down time, and shortened exhaust time and in turn enhanced production efficiency.

In the seventh aspect of the invention, an oil separator for removing refrigerator oil from the refrigerant mixture is disposed in the defrosting circuit of the ultra-low temperature freezer. Thus, it can be prevented that, during defrosting, the refrigerator oil in the refrigerant mixture is supplied from the defrosting circuit to the cooler to solidify in the cooler, and an increase in pressure loss that would be caused when a plurality of oil separators were disposed in series between the compressor and the condenser can be prevented. This provides enhanced cooling efficiency while ensuring good circulation of the refrigerant mixture.

In the eighth aspect of the invention, the oil separator is disposed between the upstream end of the defrosting circuit and the shut-off valve. Thus, when the shut-off valve is closed, it can be prevented that a pressure difference occurs between the suction side of the compressor and the oil separator, the former having a higher pressure than the latter. This prevents backflow of refrigerator oil from the suction side of the compressor toward the oil separator to smoothly return the refrigerator oil to the compressor.

According to the ninth aspect of the invention, since the oil separator is disposed in the upstream side of the defrosting circuit, even high-temperature and low-viscosity refrigerator oil can be recovered, which enables the removal of refrigerator oil with higher reliability.

According to the tenth aspect of the invention, since a plurality of buffer tanks are connected to the refrigerant circuit, the buffer tank installation space can be saved. Further, the total buffer tank capacity can be increased, which prevents abnormal increase in the discharge pressure of the compressor to provide stable operation of the freezer.

According to the eleventh aspect of the invention, since the first and second buffer tanks are connected to each other through a communicating passage, refrigerant can be moved between both the tanks. This prevents the retention of gas refrigerant in the tanks and prevents deterioration of the cooling capacity due to variations in the composition of refrigerant mixture in the freezer.

In the twelfth aspect of the invention, a communicating passage is connected partway therethrough to the side of the refrigerant circuit located toward the suction part of the compressor. Thus, in the course of gas refrigerant flowing from the refrigerant circuit into the buffer tank and returning to the suction side of the compressor, the gas refrigerant smoothly circulates in the buffer tank, which prevents the retention of gas refrigerant in the tank with higher reliability.

According to the thirteenth aspect of the invention, since the refrigerant circuit is configured to allow gas refrigerant to flow from the discharge side of the compressor into the buffer tanks and then return to the suction side of the compressor, this prevents the retention of gas refrigerant in the tanks with higher reliability.

In the fourteenth aspect of the invention, the downstream end part of the defrosting circuit in the ultra-low temperature freezer is branched into a main branch circuit and a sub-branch circuit and the main branch circuit and the sub-branch circuit are connected to one side of the refrigerant circuit toward the entrance of the cooler and the other side toward the exit of the cooler, respectively. Thus, the cooler and the heat exchanger can be concurrently raised in temperature, so that refrigerator oil or the like having passed through the cooler can be prevented from solidifying in the heat exchanger. This ensures good circulation of refrigerant in the refrigerant circuit, thereby shortening the defrosting operation time.

In the fifteenth aspect of the invention, a shut-off valve is provided in the sub-branch circuit. Thus, when refrigerator oil or the like in the heat exchanger is heated to or above the pour point at which it can flow smoothly and the shut-off valve is then closed, the refrigerant mixture can be sent only to the main branch circuit to raise the temperature of the cooler, which further shortens the defrosting operation time.

In the sixteenth aspect of the invention, part of the refrigerant circuit for supplying refrigerant from the primary side of the final-stage cascade heat exchanger to the cooler is divided into a plurality of branch circuits, pressure reducing elements are connected into the branch circuits, respectively, and the refrigerant can be distributed into the plurality of branch circuits by the operation of a selector to increase the flow rate. This shortens the cooling time taken until the cooling target reaches a predetermined cooling temperature while ensuring a required pressure reduction capability to cool the cooling target down to the predetermined cooling temperature.

According to the seventeenth aspect of the invention, since the selector comprises a shut-off valve disposed in at least one of the branch circuits, this enables flexible control on the cooling temperature and cooling time of the cooler.

According to the eighteenth aspect of the invention, since the plurality of pressure reducing elements have different pressure reduction capabilities, the control ranges of the cooling temperature and cooling time of the cooler can be widened.

According to the nineteenth aspect of the invention, since the pressure reducing element comprises a capillary tube, pressure reduction can be reliably implemented even in an ultra-low temperature range, which is advantageous for stable operation of the freezer. Further, the use of the capillary tune provides higher reliability and significantly reduced equipment cost.

According to the twentieth aspect of the invention, since moisture in a vacuum chamber of a vacuum apparatus is frozen by cooling it using the cooler of the ultra-low temperature freezer, this enhances the production efficiency and the operational stability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view schematically showing a layout of a vacuum deposition apparatus according to an embodiment of the present invention.

FIG. 2 is a plan view schematically showing another layout of the vacuum deposition apparatus.

FIG. 3 is a refrigerant system diagram showing the overall configuration of an ultra-low temperature freezer according to Embodiment 1 of the present invention.

FIG. 4 is a plan view showing in larger scale an essential part of the ultra-low temperature freezer.

FIG. 5 is a view taken in the direction of arrow V of FIG. 4.

FIG. 6 is a corresponding view of FIG. 4, showing Embodiment 2.

FIG. 7 is a corresponding view of FIG. 4, showing Embodiment 3.

FIG. 8 is a view taken in the direction of arrow VIII of FIG. 7.

FIG. 9 is a refrigerant system diagram showing the overall configuration of an ultra-low temperature freezer according to Embodiment 4 of the present invention.

FIG. 10 is a refrigerant system diagram showing the overall configuration of an ultra-low temperature freezer according to Embodiment 5 of the present invention.

FIG. 11 is a refrigerant system diagram showing the overall configuration of an ultra-low temperature freezer according to Embodiment 6 of the present invention.

FIG. 12 is a refrigerant system diagram showing the overall configuration of an ultra-low temperature freezer according to Embodiment 7 of the present invention.

FIG. 13 is a refrigerant system diagram showing the overall configuration of an ultra-low temperature freezer according to Embodiment 8 of the present invention.

FIG. 14 is a refrigerant system diagram showing the overall configuration of an ultra-low temperature freezer according to Embodiment 9 of the present invention.

FIG. 15 is a refrigerant system diagram showing the overall configuration of an ultra-low temperature freezer according to Embodiment 10 of the present invention.

FIG. 16 is a refrigerant system diagram showing the overall configuration of an ultra-low temperature freezer according to Embodiment 11 of the present invention.

FIG. 17 is a refrigerant system diagram showing the overall configuration of an ultra-low temperature freezer according to Embodiment 12 of the present invention.

FIG. 18 is a refrigerant system diagram showing the overall configuration of an ultra-low temperature freezer according to Embodiment 13 of the present invention.

EXPLANATION OF REFERENCE CHARACTERS

-   A vacuum deposition apparatus -   R ultra-low temperature freezer -   1 refrigerant circuit -   2 refrigerant pipe -   2 a main refrigerant pipe -   2 b sub refrigerant pipe -   4 compressor -   5 oil separator (first oil separator) -   6 oil return pipe -   8 water-cooled condenser (condenser) -   9 dryer -   10 auxiliary condenser (condenser) -   12 first gas-liquid separator -   13 second gas-liquid separator -   14 third gas-liquid separator -   15 fourth gas-liquid separator -   18 first heat exchanger -   19 second heat exchanger -   20 third heat exchanger -   21 fourth heat exchanger -   24 first capillary tube (pressure reducing element) -   25 second capillary tube (pressure reducing element) -   26 third capillary tube (pressure reducing element) -   27 fourth capillary tube (pressure reducing element) -   28 fifth capillary tube (supercooler pressure reducing element) -   29 sixth capillary tube 30 (main cooler pressure reducing element) -   31 supercooler -   31 a primary side -   31 b secondary side -   32 cryocoil (main cooler) -   35 branch pipe -   35 b main branch portion -   35 c sub-branch portion -   h height -   38 main refrigerant circuit -   39 sub refrigerant circuit -   44 solenoid shut-off valve -   45 defrosting circuit -   45 a main branch circuit -   45 b sub-branch circuit -   46 solenoid shut-off valve -   50 second oil separator -   59 pressure sensor -   60 buffer tank -   61 refrigerant inflow pipe -   62 refrigerant return pipe -   63 first buffer tank -   64 second buffer tank -   65 communicating passage -   66 solenoid shut-off valve -   68 solenoid shut-off valve -   80 first branch circuit -   80 a first branch capillary tube -   80 b solenoid shut-off valve -   81 second branch circuit -   81 a second branch capillary tube -   81 b solenoid shut-off valve -   82 third branch circuit -   82 a third branch capillary tube -   82 b solenoid shut-off valve -   83 fourth branch circuit -   83 a fourth branch capillary tube -   83 b solenoid shut-off valve -   100 vacuum chamber

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention are described below in detail with reference to the drawings. The following description of preferred embodiments is merely illustrative and is not intended to limit the scope, applications and use of the invention.

Embodiment 1

FIG. 1 shows an example of the layout of a vacuum deposition apparatus A serving as a vacuum apparatus according to an embodiment of the invention. Reference numeral 100 denotes a vacuum chamber in which films are deposited on unshown substrates (also referred to as wafers) with the inside kept under vacuum. The vacuum chamber 100 has a carry-in-and-out opening (not shown) that can be opened and closed by an opening and closing door 101. Substrates on which films are to be deposited are carried in the vacuum chamber 100 or the substrates on which films have been deposited are carried out of it, in each case with the opening and closing door 101 open. The vacuum chamber 100 is connected through a communicating passage 102 with a vacuum pump 103. A gate valve 104 is disposed at the connecting point of the communicating passage 102 and the vacuum chamber 100 to switch between providing flow communication between them and interrupting the flow communication of them by turning the valve on/off. The vacuum chamber 100 is vacuumized by activating the vacuum pump 103 with the opening and closing door 101 closed and the gate valve 104 open.

The above vacuum deposition apparatus A is provided with an ultra-low temperature freezer R constituting a refrigeration system according to Embodiment 1 of the present invention. The vacuum deposition apparatus A is configured to trap moisture serving as a cooling target in the vacuum chamber 100 through freezing by directly cooling the moisture down to an ultra-low temperature level by the later-described cryocoil 32 in the ultra-low temperature freezer R with the vacuum chamber 100 vacuumized by the vacuum pump 103 and thereby raise the vacuum level in the vacuum chamber 100.

In contrast, FIG. 2 shows another example of the layout of the vacuum deposition apparatus A, in which the cryocoil 32 in the freezer R is disposed not in the vacuum chamber 100 but partway through the communicating passage 102. The vacuum deposition apparatus A is configured to trap moisture in the vacuum chamber 100 through freezing by cooling moisture in the communicating passage 102, i.e., indirectly cooling the moisture in the vacuum chamber 100, by the ultra-low temperature freezer R with the vacuum chamber 100 vacuumized by the vacuum pump 103 and thereby raise the vacuum level in the vacuum chamber 100. The rest of the configuration is the same as for the vacuum deposition apparatus A shown in FIG. 1.

The ultra-low temperature freezer R uses as a refrigerant a non-azeotropic refrigerant mixture obtained by mixing plural kinds of refrigerants of different boiling temperatures to thereby create a cold environment at an ultra-low temperature level of −100° C. or below.

Specifically, FIG. 3 shows the overall configuration of the ultra-low temperature freezer R. Reference numeral 1 denotes a closed-cycle refrigerant circuit charged with the above refrigerant mixture. The refrigerant circuit 1 is formed by connecting various elements described below to each other through a refrigerant pipe 2. Reference numeral 4 denotes a compressor for compressing gas refrigerant. The compressor 4 is connected at a discharge part thereof to an oil separator 5. The oil separator 5 is for separating refrigerator oil, such as lubricating oil for a compressor, mixed into gas refrigerant discharged by the compressor 4 from the gas refrigerant. The separated refrigerator oil is returned through an oil return pipe 6 to the suction side of the compressor 4. The oil separator 5 is connected at a refrigerant discharge part thereof to a water-cooled condenser 8 for cooling gas refrigerant discharged from the compressor 4 by heat exchange with cooling water in a cooling water passage 7 to condense it. The water-cooled condenser 8 is connected at a discharge part thereof to the primary side of an auxiliary condenser 10 through a dryer 9 for removing moisture and contamination in the refrigerant. In the auxiliary condenser 10, gas refrigerant from the water-cooled condenser 8 is cooled and condensed by heat exchange with low-temperature refrigerant that is returning through the secondary side of the auxiliary condenser 10 and will be sucked later into the compressor 4. In this embodiment, the water-cooled condenser 8 and the auxiliary condenser 10 constitute a condenser of the invention. Both the condensers 8, 10 condense gas refrigerant of relatively high boiling temperature in the refrigerant mixture to liquefy it.

The auxiliary condenser 10 is connected at a discharge part of the primary side to a first gas-liquid separator 12 and the first gas-liquid separator 12 separates gas-liquid mixture refrigerant coming from the auxiliary condenser 10 into liquid refrigerant and gas refrigerant. The first gas-liquid separator 12 is connected at a gas refrigerant discharge part thereof to the primary side of a first heat exchanger 18 of cascade type heat exchangers and connected at a liquid refrigerant discharge part thereof to the secondary side of the first heat exchanger 18 through a first capillary tube 24 serving as a pressure reducing element. The liquid refrigerant separated by the first gas-liquid separator 12 is reduced in pressure by the first capillary tube 24 and then supplied to the secondary side of the first heat exchanger 18 to evaporate itself. The evaporation of the liquid refrigerant causes the gas refrigerant in the primary side of the first heat exchanger 18 to be cooled to condense a gaseous refrigerant component having the next highest boiling temperature in the refrigerant mixture and thereby liquefy it.

Furthermore, the first heat exchanger 18 is connected at a discharge part of the primary side to a second gas-liquid separator 13 and the second gas-liquid separator 13 separates gas-liquid mixture refrigerant coming from the first heat exchanger 18 into liquid refrigerant and gas refrigerant. The second gas-liquid separator 13 is connected at a gas refrigerant discharge part thereof to the primary side of a second heat exchanger 19 of the cascade type heat exchangers and connected at a liquid refrigerant discharge part thereof to the secondary side of the second heat exchanger 19 through a second capillary tube 25 serving as a pressure reducing element. The liquid refrigerant separated by the second gas-liquid separator 13 is reduced in pressure by the second capillary tube 25 and then supplied to the secondary side of the second heat exchanger 19 to evaporate itself. The evaporation of the liquid refrigerant causes the gas refrigerant in the primary side of the second heat exchanger 19 to be cooled to condense a gaseous refrigerant component having the next highest boiling temperature in the refrigerant mixture and thereby liquefy it.

Furthermore, like the above connecting structure, the second heat exchanger 19 is connected at a discharge part of the primary side to a third gas-liquid separator 14 and then a third heat exchanger 20 and a third capillary tube 26 and the third heat exchanger 20 is connected at a discharge part of the primary side to a fourth gas-liquid separator 15 and then a fourth heat exchanger 21 and a fourth capillary tube 27, (where these connecting structures are the same as that between the first gas-liquid separator 12, the first heat exchanger 18 and the first capillary tube 24 and, therefore, a detailed description is not given to them). The liquid refrigerant separated by the third gas-liquid separator 14 is reduced in pressure by the third capillary tube 26 and then supplied to the secondary side of the third heat exchanger 20 to evaporate itself. The evaporation of the liquid refrigerant causes the gas refrigerant coming from the third gas-liquid separator 14 and flowing through the primary side of the third heat exchanger 20 to be cooled to condense a gaseous refrigerant component having the next highest boiling temperature in the refrigerant mixture and thereby liquefy it. Further, the liquid refrigerant separated by the fourth gas-liquid separator 15 is reduced in pressure by the fourth capillary tube 27 and then supplied to the secondary side of the fourth heat exchanger 21 to evaporate itself. The evaporation of the liquid refrigerant causes the gas refrigerant coming from the fourth gas-liquid separator 15 and flowing through the primary side of the fourth heat exchanger 21 to be cooled to condense a remaining gaseous refrigerant component in the refrigerant mixture and thereby liquefy it.

Furthermore, the fourth heat exchanger 21 is connected at a discharge part of the primary side to the primary side 31 a of a supercooler (sub-cooler) 31 formed of a heat exchanger. Part of the refrigerant pipe 2 connected to a discharge part of the primary side 31 a of the supercooler 31 is branched on its way into a main refrigerant pipe 2 a and a sub refrigerant pipe 2 b through a branch pipe 35.

The sub refrigerant pipe 2 b is provided with a fifth capillary tube (a supercooler pressure reducing element) 28 connected partway therethrough. The downstream end of the sub refrigerant pipe 2 b is connected to the secondary side 31 b of the supercooler 31 and the secondary side 31 b of the supercooler 31 is connected through the refrigerant pipe 2 to the secondary side of the fourth heat exchanger 21. Thus, the refrigerant discharged from the fourth heat exchanger 21 passes through the primary side 31 a of the supercooler 31. Then, part of the refrigerant is reduced in pressure by the fifth capillary tube 28 in the sub refrigerant pipe 2 b and the obtained liquid refrigerant is supplied to the secondary side 31 b of the supercooler 31 to evaporate itself. The heat of evaporation of the liquid refrigerant causes gas refrigerant in the primary side 31 a of the supercooler 31 to be cooled.

On the other hand, the main refrigerant pipe 2 a is provided with a sixth capillary tube 29 serving as a main cooler pressure reducing element and a cryocoil 32 both connected partway therethrough and in series in order from upstream to downstream side. The cryocoil 32 constitutes a main cooler and, as shown in FIG. 1 or 2, cools moisture, serving as an cooling target, in the vacuum chamber 100. The downstream end of the main refrigerant pipe 2 a is connected to part of the refrigerant pipe 2 located between the secondary side of the fourth heat exchanger 21 and the secondary side 31 b of the supercooler 31. Thus, the rest of the refrigerant discharged from the primary side 31 a of the supercooler 31 is reduced in pressure by the sixth capillary tube 29 in the main refrigerant pipe 2 a and supplied to the cryocoil 32 to evaporate itself. The heat of evaporation of the refrigerant causes moisture (cooling target) in the vacuum chamber 100 to be cooled down to an ultra-low temperature level of −100° C. or below to trap the moisture by freezing, which raises the vacuum level of the vacuum chamber 100.

Furthermore, the secondary side of the supercooler 31 (and the cryocoil 32) are connected in series with the secondary sides of the fourth heat exchanger 21, the third heat exchanger 20, the second heat exchanger 19, the first heat exchanger 18 and the auxiliary condenser 10 in this order through the refrigerant pipe 2. The secondary side of the auxiliary condenser 10 is further connected to the suction side of the compressor 4. Thus, gasified refrigerant components in the refrigerant mixture obtained through evaporation in the above elements, respectively, are sucked into the compressor 4.

One feature of the invention is the location and/or structure of the branch pipe 35. Specifically, as shown in magnified form in FIGS. 4 and 5, the branch pipe 35 is composed of a collecting portion 35 a and a pair of main and sub-branch portions 35 b, 35 c bifurcated from the collecting portion 35 a. The collecting portion 35 a is joined in gastight manner to the downstream end of a portion of the refrigerant pipe 2 connected at the other end to the discharge part of the primary side 31 a of the supercooler 31, by brazing or other means of attachment. The main branch portion 35 b and the sub-branch portion 35 c are joined in gastight manner to the upstream end of the main refrigerant pipe 2 a and the upstream end of the sub refrigerant pipe 2 b, respectively, by brazing or other means of attachment. These main refrigerant pipe 2 a and sub refrigerant pipe 2 b extend substantially along the horizontal plane. A main refrigerant circuit 38 is formed inside the main branch portion 35 b and inside the main refrigerant pipe 2 a, while a sub refrigerant circuit 39 is formed inside the sub-branch portion 35 c and inside the sub refrigerant pipe 2 b.

The main branch portion 35 b and sub-branch portion 35 c of the branch pipe 35 have equal diameters (both the same outer diameter and the same inner diameter). The main refrigerant pipe 2 a connected to the main branch portion 35 b and the sub refrigerant pipe 2 b connected to the sub-branch portion 35 c are made of pipes having equal inner diameters. The main branch portion 35 b and the sub-branch portion 35 c are vertically juxtaposed substantially along the vertical plane so that the sub-branch portion 35 c is located below the main branch portion 35 b. The sub-branch portion 35 c and the connected sub refrigerant pipe 2 b are placed a predetermined height h lower than the main branch portion 35 b and the connected main refrigerant pipe 2 a. Thus, the height of the whole sub refrigerant circuit 39 is set lower than the height of the whole main refrigerant circuit 38.

In FIG. 3, reference numeral 44 denotes a solenoid shut-off valve connected to the main refrigerant pipe 2 a between the sixth capillary tube 29 and the cryocoil 32, reference numeral 45 denotes a defrosting circuit connected to the main refrigerant pipe 2 a between the solenoid shut-off valve 44 and the cryocoil 32 and connected to the refrigerant pipe 2 between the oil separator 5 and the water-cooled condenser 8, and reference numeral 46 denotes a solenoid shut-off valve connected partway through the defrosting circuit 45. During the normal operation in which films are deposited on substrates in the vacuum chamber 100 of the vacuum deposition apparatus A with the vacuum chamber 100 put under vacuum, the solenoid shut-off valve 46 is closed to close the defrosting circuit 45 and the solenoid shut-off valve 44 is opened to open the main refrigerant pipe 2 a. Thus, a low-boiling refrigerant component is evaporated by the cryocoil 32 to cool moisture in the vacuum chamber 100 and thereby trap it by freezing. On the other hand, during the defrosting operation in which the opening and closing door 101 is opened to open the vacuum chamber 100 to the atmosphere and film deposition on substrates are not carried out, the solenoid shut-off valve 46 is opened to open the defrosting circuit 45 and the solenoid shut-off valve 44 is closed to close the main refrigerant circuit 2 a. Thus, high-temperature gas refrigerant (hot gas) discharged from the compressor 4 is supplied through the defrosting circuit 45 to the cryocoil 32 as it is, thereby turning the moisture trapped and frozen by the cryocoil 32 back to the former state.

Further, reference numeral 60 denotes a buffer tank. The buffer tank 60 is connected through a refrigerant inflow pipe 61 to the refrigerant pipe 2 between the gas refrigerant discharge part of the first gas-liquid separator 12 and the primary side of the first heat exchanger 18. The buffer tank 60 is also connected, to part of the refrigerant pipe 2 communicating with the suction side of the compressor 4, through a refrigerant return pipe 62 for returning gas refrigerant in the buffer tank 60 to the suction side of the compressor 4. Thus, the buffer tank 60 prevents that at the start of operation of the freezer R insufficiently condensed gas refrigerant abnormally increases the discharge pressure of the compressor 4.

Furthermore, first to third manual shut-off valves 71 to 73 are disposed in the vicinity of the solenoid shut-off valve 46 in the defrosting circuit 45, in the vicinity of the solenoid shut-off valve 44 between the sixth capillary tube 29 and the cryocoil 32 and in the refrigerant pipe 2 between the exit of the cryocoil 32 and the secondary side of the fourth heat exchanger 21, respectively. These first to third manual shut-off valves 71 to 73 are individually closed during replacement or maintenance of the cryocoil 32 to prevent the refrigerant mixture remaining in the pipes from leaking out.

Furthermore, a refrigerant supply line 70 for supplying the refrigerant mixture into the refrigerant circuit 1 is connected to the refrigerant pipe 2 between the exit of the cryocoil 32 and the secondary side of the fourth heat exchanger 21. The refrigerant supply line 70 also serves as a discharge line for discharging the refrigerant mixture from the refrigerant circuit 1. The refrigerant supply line 70 is provided with a supply shut-off valve 75 that is opened during supply or discharge of the refrigerant.

In FIG. 4, reference numeral 42 denotes a strainer connected in series between the sub-branch portion 35 c of the branch pipe 35 and the fifth capillary tube 28 (though it is not shown in FIG. 3).

Consequently, in this embodiment, when films are deposited on substrates in the vacuum chamber 100 of the vacuum deposition apparatus A, the ultra-low temperature freezer R is operated so that moisture in the vacuum chamber 100 (or in the communicating passage 102) is cooled down to an ultra-low temperature level of −100° C. or below and thereby trapped by freezing, resulting in putting the vacuum chamber 100 under vacuum.

More specifically, during operation of the ultra-low temperature freezer R, the solenoid shut-off valve 46 is closed to close the defrosting circuit 45 and the solenoid shut-off valve 44 is opened to open the main refrigerant pipe 2 a. Thus, the refrigerant mixture discharged from the compressor 4 is cooled by the water-cooled condenser 8 and then cooled in the auxiliary condenser 10 by the refrigerant flowing through the secondary side thereof and returning to the compressor 4, so that the refrigerant mixture, mainly the highest-boiling gaseous refrigerant component, is condensed and thereby liquefied. The refrigerant mixture is separated into gas refrigerant and liquid refrigerant in the first gas-liquid separator 12. The liquid refrigerant is reduced in pressure by the first capillary tube 24 and then evaporates in the primary side of the first heat exchanger 18. The heat of evaporation causes the gas refrigerant from the first gas-liquid separator 24 to be cooled so that mainly the highest-boiling gaseous refrigerant component in the gas refrigerant is condensed and thereby liquefied. In subsequent stages, likewise, the second to fourth heat exchangers 19 to 21 sequentially condenses and liquefies gaseous refrigerant components in the refrigerant mixture in order from higher- to lower-boiling refrigerant components.

The refrigerant discharged from the primary side of the fourth heat exchanger 21 is in a gas-liquid mixture state. This gas-liquid mixture refrigerant passes through the primary side 31 a of the supercooler 31 and is then distributed at the branch pipe 35 into two paths, i.e., the main refrigerant circuit 38 (main refrigerant pipe 2 a) and the sub refrigerant circuit 39 (sub refrigerant pipe 2 b). The refrigerant having flowed into the sub refrigerant circuit 39 is reduced in pressure by the fifth capillary tube 28 and then supplied to the secondary side 31 b of the supercooler 31 to evaporate itself. The heat of evaporation causes further cooling of the gas-liquid mixture refrigerant supplied from the fourth heat exchanger 21 to the primary side 31 a of the supercooler 31 so that the amount of liquid refrigerant is increased.

The rest of the gas-liquid mixture refrigerant, which having flowed into the main refrigerant pipe 2 a after discharged from the primary side 31 a of the supercooler 31, is reduced in pressure by the sixth capillary tube 29 and then evaporates in the cryocoil 32 to apply a cold environment of, for example, −100° C. or below, to moisture in the vacuum chamber 100. Owing to the cold environment of −100° C. or below, the moisture in the vacuum chamber 100 is trapped by freezing to raise the vacuum level in the vacuum chamber 100.

The sub refrigerant circuit 39 is lower in height than the main refrigerant circuit 39. Therefore, when the gas-liquid mixture refrigerant having passed through the fourth heat exchanger 21 and the primary side 31 a of the supercooler 31 is divided at the branch pipe 35 into the main refrigerant circuit 38 (main refrigerant pipe 2 a) and the sub refrigerant circuit 39 (sub refrigerant pipe 2 b), liquid refrigerant of the gas-liquid mixture refrigerant flows more into the sub refrigerant circuit 39 of relatively small height. Therefore, the flow rate of liquid refrigerant into the sub refrigerant circuit 39 becomes higher than that of liquid refrigerant into the main refrigerant circuit 38. This provides sufficient cooling of gas refrigerant in the primary side 31 a of the supercooler 31, which increases the flow rate of liquid refrigerant obtained by the gas refrigerant liquefaction of the supercooler 31 and thereby enhances the cooling efficiency of the cryocoil 32. Additionally, even if the heat load in the vacuum chamber 100 varies during film deposition, the inside of the vacuum chamber 100 can be stably cooled. Therefore, the vacuum condition in the vacuum chamber 100 can be stably held to improve the quality of film deposition on substrates.

On the other hand, during defrosting operation in which the vacuum chamber 100 of the deposition apparatus A is left open to the atmosphere and film deposition on substrates is not carried out, the solenoid shut-off valve 46 is opened to open the defrosting circuit 45 and the solenoid shut-off valve 44 is closed to close the main refrigerant pipe 2 a. Thus, the high-temperature gas refrigerant discharged from the compressor 4 is supplied through the defrosting circuit 45 to the cryocoil 32 so that moisture in the cryocoil 32 is defrosted. When the vacuum chamber 100 is returned back to a vacuum condition after the defrosting operation, in like manner, the solenoid shut-off valve 46 is closed to close the defrosting circuit 45 and the solenoid shut-off valve 44 is opened to open the main refrigerant pipe 2 a, so that a low-boiling refrigerant component discharged from the primary side 31 a of the supercooler 31 is distributed at the branch pipe 35 into the main refrigerant circuit 38 and the sub refrigerant circuit 39. Also in this case, owing to the above-mentioned height difference h between the main refrigerant circuit 38 and the sub refrigerant circuit 39, the flow rate of liquid refrigerant into the secondary side 31 b of the supercooler 31 becomes higher than that into the cryocoil 32. Therefore, the inside of the vacuum chamber 100 can be quickly cooled from normal to ultra-low temperature level. This shortens the cool-down time and in turn provides shortened time of exhaust from the vacuum chamber 100, shortened process time for film deposition and enhanced efficiency of film deposition.

Further, in order to enhance the cooling efficiency of the cryocoil 32, it suffices to create a height difference between the main refrigerant circuit 38 and the sub refrigerant circuit 39. Therefore, the above effects can be obtained with a simple structure.

In this embodiment, the height of the whole sub refrigerant circuit 39 is made lower than that of the whole main refrigerant circuit 38 by extending both the main refrigerant circuit 38 and the sub refrigerant circuit 39 along the horizontal plane. Such a height difference, however, need not be created over the whole lengths of the main refrigerant circuit 38 and the sub refrigerant circuit 39. It is necessary that at least at the bifurcation of the main refrigerant circuit 38 and the sub refrigerant circuit 39, the maximum height of the sub refrigerant circuit 39 is lower than the minimum height of the main refrigerant circuit 38.

Embodiment 2

FIG. 6 shows Embodiment 2 of the invention (where the same parts as in FIGS. 1 to 5 in this and following embodiments are identified by the same reference characters and a detailed description thereof is not given). In Embodiment 1, the flow rate of liquid refrigerant into the secondary side 31 b of the supercooler 31 is kept higher than that into the cryocoil 32 by setting the height of the sub refrigerant circuit 39 to be lower than that of the main refrigerant circuit 38. In contrast, in this embodiment, the sub refrigerant circuit 39 and the main refrigerant circuit 38 are located at the same height but the sub refrigerant circuit 39 has a larger cross sectional area than the main refrigerant circuit 38.

More specifically, in this embodiment, in contrast to Embodiment 1, the collecting portion 35 a and main branch portion 35 b of the branch pipe 35, the main refrigerant pipe 2 a connected to these portions, the sub-branch portion 35 c of the branch pipe 35, and the sub refrigerant pipe 2 b connected to the sub-branch portion 35 c are all placed in the same horizontal plane, i.e., at the same height.

Further, while the main branch portion 35 b and sub-branch portion 35 c of the branch pipe 35 have the same diameter as in Embodiment 1, a pipe having a smaller diameter than the sub refrigerant pipe 2 b connected to the sub-branch portion 35 c is used as the main refrigerant pipe 2 a connected to the main branch portion 35 b. Thus, the sub refrigerant circuit 39 formed inside the sub-branch portion 35 c and inside the sub refrigerant pipe 2 b has a larger cross sectional area than the main refrigerant circuit 38 formed inside the main branch portion 35 b and inside the main refrigerant pipe 2 a.

The rest of the configuration is the same as Embodiment 1. Though the strainer 42 and the fifth capillary tube 28 are not shown in FIG. 6, they have the same structures as in Embodiment 1 (see FIG. 4).

In this embodiment, a pipe having a narrower diameter than the sub refrigerant pipe 2 b is used as the main refrigerant pipe 2 a so that the sub refrigerant circuit 39 has s larger cross sectional area than the main refrigerant circuit 38. Thus, when the refrigerant discharged from the primary side 31 a of the supercooler 31 is distributed into the main refrigerant circuit 38 and the sub refrigerant circuit 39, the flow rate of gas-liquid mixture refrigerant into the sub refrigerant circuit 39, taken as a whole, becomes higher than that of gas-liquid mixture refrigerant into the main refrigerant circuit 38. Therefore, the flow rate of liquid refrigerant into the sub refrigerant circuit 39 becomes proportionately higher than that of liquid refrigerant into the main refrigerant circuit 38. This provides sufficient cooling of gas refrigerant in the primary side 31 a of the supercooler 31, which increases the flow rate of liquid refrigerant obtained by the gas refrigerant liquefaction of the supercooler 31 and thereby enhances the cooling efficiency of the main cooler. Consequently, the same effects as Embodiment 1 can be obtained.

In Embodiment 2, the sub refrigerant pipe 2 b is made thicker than the main refrigerant pipe 2 a by using a pipe of a normal diameter, as in Embodiment 1, as the sub refrigerant pipe 2 b and using a narrower pipe as the main refrigerant pipe 2 a. The same objective can be achieved, on the contrary, by using a pipe of a normal diameter as the main refrigerant pipe 2 a and using a thicker pipe as the sub refrigerant pipe 2 b.

Also in Embodiment 2, the sub refrigerant circuit 39 has a larger cross sectional area for the whole length than the main refrigerant circuit 38. Such a cross sectional area difference, however, need not be created over the whole lengths of the sub refrigerant circuit 39 and the main refrigerant circuit 38. It suffices if the minimum cross sectional area of the sub refrigerant circuit 39 is larger than the maximum cross sectional area of the main refrigerant circuit 38.

Embodiment 3

FIGS. 7 and 8 show Embodiment 3, which is a combination of technical matters of Embodiments 1 and 2. Specifically, in this embodiment, like Embodiment 1, the main branch portion 35 b and sub-branch portion 35 c of the branch pipe 35 are vertically juxtaposed substantially along the vertical plane so that the sub-branch portion 35 c is located below the main branch portion 35 b, and the sub-branch portion 35 c and the sub refrigerant pipe 2 b connected thereto are located at a lower height than the main branch portion 35 b and the main refrigerant pipe 2 a connected thereto. Further, like Embodiment 2, a narrower pipe than the sub refrigerant pipe 2 b connected to the sub-branch portion 35 c of the branch pipe 35 is used as the main refrigerant pipe 2 a connected to the main branch portion 35 b of the branch pipe 35 so that the sub refrigerant circuit 39 has a larger cross sectional area than the main refrigerant circuit 38 formed inside the main branch portion 35 b and inside the main refrigerant pipe 2 a. The rest of the configuration is the same as in Embodiment 1 or 2.

Thus, in this embodiment, the behaviors and effects of Embodiments 1 and 2 synergistically act to further enhance the cooling efficiency of the cryocoil 32.

Also in this embodiment, like Embodiment 1, it is necessary that at least at the bifurcation of the main refrigerant circuit 38 and the sub refrigerant circuit 39, the maximum height of the sub refrigerant circuit 39 is lower than the minimum height of the main refrigerant circuit 38.

The above Embodiments 1 to 3 are applied to refrigeration systems using non-azeotropic refrigerant mixture obtained by mixing plural kinds of refrigerants. The present invention is, however, applicable to refrigeration systems using no refrigerant mixture. All that is required is that the refrigeration system includes a supercooler as well as a main cooler.

Embodiment 4

FIG. 9 shows the overall configuration of an ultra-low temperature freezer R according to Embodiment 4 of the invention. In the following Embodiments 4 to 13, the structure of the branch pipe 35 described in Embodiments 1 to 3 is not essential.

Embodiment 4 is characterized by the configuration of the defrosting circuit 45. Specifically, as shown in FIG. 9, a second oil separator 50 for separating refrigerator oil, such as lubrication oil for a compressor, from gas refrigerant is disposed between the upstream end of the defrosting circuit 45 and the solenoid shut-off valve 46 (and the oil separator 5 connected to the discharge part of the compressor 4 is referred to as a first oil separator). The refrigerator oil separated by the second oil separator 50 is returned, as with the first oil separator 5, through the oil return pipe 6 to the suction side of the compressor 4. The second oil separator 50 is disposed at a location along the defrosting circuit 45 at which the distance to the upstream end thereof is shorter than that to the downstream end thereof (i.e., somewhere in the upstream half of the defrosting circuit 45) so that refrigerator oil of high temperature and low viscosity can be separated out to ensure the removal of the refrigerator oil. The rest of the configuration is the same as in Embodiment 1.

In this embodiment, the defrosting circuit 45 is provided with the second oil separator 50 for removing refrigerator oil from the refrigerant mixture. Therefore, when, during defrosting operation in which film deposition on substrates is not carried out in the vacuum chamber 100 of the deposition apparatus A, the solenoid shut-off valve 44 is closed and the solenoid shut-off valve 46 is opened so that the refrigerant mixture discharged from the compressor 4 is supplied through the defrosting circuit 45 to the cryocoil 32, the refrigerator oil in the refrigerant mixture, though it cannot completely be removed by the first oil separator 5, can be further removed by the second oil separator 50. Thus, it can be prevented that the refrigerator oil is supplied through the defrosting circuit 45 to the cryocoil 32. Further, it can be prevented that particularly at the start of defrosting operation, the refrigerator oil is cooled and solidified in the cryocoil 32 still at an ultra-low temperature level. This ensures good circulation of the refrigerant mixture and in turn provides shortened time of exhaust from the vacuum chamber 100, shortened process time for film deposition and enhanced efficiency of film deposition.

Further, the second oil separator 50 is disposed at a location along the defrosting circuit 45 at which the distance to the upstream end of the defrosting circuit 45 is shorter than that to the downstream end thereof. This is advantageous in separating refrigerator oil of high temperature and low viscosity and thereby further ensures the removal of the refrigerator oil.

Furthermore, when the inside of the vacuum chamber 100 is returned back to a vacuum condition after such a defrosting operation, the solenoid shut-off valve 44 is opened and the solenoid shut-off valve 46 is closed so that the refrigerator oil separated by the second oil separator 50 is recovered to the suction side of the compressor 4. At this time, since the second oil separator 50 is disposed between the upstream end of the defrosting circuit 45 and the solenoid shut-off valve 46, it can be prevented that a pressure difference occurs between the suction side of the compressor 4 and the second oil separator 50, with the former having a higher pressure than the latter. Thus, it can be prevented that the refrigerator oil flows from the suction side of the compressor 4 back to the second oil separator 50. This provides a smooth return flow of the refrigerator oil to the compressor 4.

Embodiment 5

FIG. 10 shows the overall configuration of an ultra-low temperature freezer R according to Embodiment 5 of the invention. This embodiment is characterized by the circuit configuration of buffer tanks. Specifically, referring to FIG. 10, the compressor 4 is connected at its discharge part to a pressure sensor 59 for detecting the gas refrigerant discharge pressure. Reference numeral 63 denotes a first buffer tank and reference numeral 64 denotes a second buffer tank located below the first buffer tank 63. At the start of operation of the ultra-low temperature freezer R, these first and second buffer tanks 63, 64 temporarily release insufficiently condensed, high-pressure gas refrigerant to prevent abnormal increase in the discharge pressure of the compressor 4.

The first and second buffer tanks 63, 64 are connected to each other through a communicating passage (communicating pipe) 65 for providing flow communication of gas refrigerant between both the tanks 63, 64. The second buffer tank 64 is connected through the refrigerant inflow pipe 61 to the refrigerant pipe 2 between the gas refrigerant discharge part of the first gas-liquid separator 12 and the primary side of the first heat exchanger 18. A solenoid shut-off valve 66 is connected into the refrigerant inflow pipe 61 to control the flow of gas refrigerant into the first and second buffer tank 63, 64. The refrigerant inflow pipe 61 is also connected partway therealong (at a location between the solenoid shut-off valve 66 and the second buffer tank 64) to a refrigerant return pipe 62 for returning the gas refrigerant in the first and second buffer tanks 63, 64 to part of the refrigerant pipe 2 communicating with the suction side of the compressor 4.

Further, a fusible plug 67 is connected to the bottom of the first buffer tank 63. The fusible plug 67 is for fusing itself by the heat of a fire or the like to open the first buffer tank 63 to the atmosphere and thereby reduce the internal pressure of the tank. The rest of the configuration is the same as in Embodiment 4.

Thus, in this embodiment, if at the start of operation of the ultra-low temperature freezer R, insufficiently condensed gas refrigerant causes an abnormal increase in the discharge pressure of the compressor 4, this is detected by the pressure sensor 59. On the detection, the solenoid shut-off valve 66 is opened so that part of gas refrigerant separated by the first gas-liquid separator 12 flows through the refrigerant inflow pipe 61 into the second buffer tank 64. Further, if the amount of inflow of the gas refrigerant into the second buffer tank 64 is large, the gas refrigerant also flows through the communicating passage 65 into the first buffer tank 63. Then, when the abnormal increase in the discharge pressure is eliminated, this is detected by the same pressure sensor 59. Thus, the solenoid shut-off valve 66 is closed so that the gas refrigerant is returned from the first and second buffer tanks 63, 64 through the refrigerant return pipe 62 into the part of the refrigerant pipe 2 communicating with the suction side of the compressor 4.

In this case, since, as described above, two buffer tanks, i.e., the first and second buffer tanks 63, 64 are connected to the refrigerant circuit 1, the buffer tank installation space can be easily saved as compared with where a single large-capacity buffer tank is connected to the circuit to eliminate shortage of capacity of the buffer tank.

Furthermore, since the first and second buffer tanks 63, 64 are connected to each other through the communicating passage 65, gas refrigerant is moved between both the tanks 63, 64 to prevent the retention of gas refrigerant in each of the buffer tanks 63, 64. Thus, all the refrigerant components of different specific gravities can be circulated throughout the refrigerant circuit to prevent the deterioration of the cooling capacity due to variations in the composition of the refrigerant mixture in the freezer R.

If solenoid shut-off valves are connected into the refrigerant return pipe 62 as well as the refrigerant inflow pipe 61, respectively, to open or close each solenoid shut-off valve according to abnormal increase in the discharge pressure of the compressor 4, this can control the amount of gas refrigerant flowing into the first and second buffer tanks 63, 64 or the amount of gas refrigerant returned from the first and second buffer tanks 63, 64 to the refrigerant circuit 1. Further, the number of buffer tanks provided may be three or more. These matters also apply to the following Embodiments 6 and 7.

Embodiment 6

FIG. 11 shows a refrigerant circuit of an ultra-low temperature freezer R according to Embodiment 6 of the invention. The difference of this embodiment from Embodiment 5 lies just in the circuit configuration for the first and second buffer tanks 63, 64. Therefore, the same parts as in Embodiment 5 are identified by the same reference characters and a description is given only to different points (the same is true of Embodiment 7).

The first and second buffer tanks 63, 64 are connected to each other, like Embodiment 5, through the communicating passage 65 for providing flow communication of gas refrigerant between both the tanks 63, 64. In contrast, unlike Embodiment 5, the first buffer tank 63 is connected through the refrigerant inflow pipe 61 to the refrigerant pipe 2 between the gas refrigerant discharge part of the first gas-liquid separator 12 and the primary side of the first heat exchanger 18. Further, the communicating passage 65 is connected partway therealong to the refrigerant return pipe 62 for returning the gas refrigerant in the first and second buffer tanks 63, 64 to part of the refrigerant pipe 2 communicating with the suction side of the compressor 4. Furthermore, the fusible plug 67 is connected to the second buffer tank 64. The rest of the configuration is the same as in Embodiment 5.

In this embodiment, if at the start of operation of the ultra-low temperature freezer R, the pressure sensor 59 detects an occurrence of an abnormal increase in the discharge pressure of the compressor 4 due to insufficiently condensed gas refrigerant, the solenoid shut-off valve 66 is opened so that part of gas refrigerant separated by the first gas-liquid separator 12 flows through the refrigerant inflow pipe 61 into the first buffer tank 63. Then, the part of gas refrigerant having flowed into the first buffer tank 63 passes through the communicating passage 65 into the second buffer tank 64. The rest of gas refrigerant is returned through the refrigerant return pipe 62 to the part of the refrigerant pipe 2 communicating with the suction side of the compressor 4.

Then, when the pressure sensor 59 detects that the abnormal increase in the discharge pressure has been eliminated, the solenoid shut-off valve 66 is closed so that the gas refrigerant in the first and second buffer tanks 63, 64 is returned through the refrigerant return pipe 62 into the part of the refrigerant pipe 2 communicating with the suction side of the compressor 4.

As described above, the communicating passage 65 is connected partway therealong to part of the refrigerant pipe 2 (refrigerant circuit 1) communicating with the suction side of the compressor 4. Therefore, in the course of gas refrigerant flowing from the refrigerant circuit 1 into the first buffer tank 63 and returning to the suction side of the compressor 4, the gas refrigerant smoothly flows through the first and second buffer tanks 63, 64. This prevents the retention of gas refrigerant in the buffer tanks 63, 64 to provide circulation of all the refrigerant components of different specific gravities throughout the refrigerant circuit, which prevents the deterioration of the cooling capacity due to variations in the composition of the refrigerant mixture in the freezer R.

The spatial relation between the first and second buffer tanks 63, 64 in Embodiment 6 is not limited to the placement of the second buffer tank 64 below the first buffer tank 63 as in Embodiment 5. For example, the first and second buffer tanks 63, 64 located the former above the latter may be replaced with each other or the first and second buffer tanks 63, 64 may be arranged laterally. The same is true of the following Embodiment 7.

Embodiment 7

FIG. 12 shows a refrigerant circuit of an ultra-low temperature freezer R according to Embodiment 7 of the invention. The difference of this embodiment from Embodiment 5 or 6 lies just in the circuit configuration for the first and second buffer tanks 63, 64.

Specifically, the first and second buffer tanks 63, 64 are connected to each other, like Embodiment 5 or 6, through the communicating passage 65 for providing flow communication of gas refrigerant between both the tanks 63, 64. Further, like Embodiment 6, the first buffer tank 63 is connected through the refrigerant inflow pipe 61 to the refrigerant pipe 2 between the gas refrigerant discharge part of the first gas-liquid separator 12 and the primary side of the first heat exchanger 18. In contrast, unlike Embodiment 6, the second buffer tank 64 is connected through the refrigerant return pipe 62 to part of the refrigerant pipe 2 communicating with the suction side of the compressor 4. Furthermore, the fusible plug 67 is connected to the second buffer tank 64. The rest of the configuration is the same as in Embodiment 6.

In this embodiment, if at the start of operation of the ultra-low temperature freezer R, the pressure sensor 59 detects an occurrence of an abnormal increase in the discharge pressure of the compressor 4 due to insufficiently condensed gas refrigerant, the solenoid shut-off valve 66 is opened so that part of gas refrigerant separated by the first gas-liquid separator 12 flows through the refrigerant inflow pipe 61 into the first buffer tank 63. Then, the part of gas refrigerant flows through the communicating passage 65 into the second buffer tank 64 and is then returned through the refrigerant return pipe 62 to the part of the refrigerant pipe 2 communicating with the suction side of the compressor 4.

Then, when the pressure sensor 59 detects that the abnormal increase in the discharge pressure has been eliminated, the solenoid shut-off valve 66 is closed so that the gas refrigerant in the first and second buffer tanks 63, 64 is returned through the refrigerant return pipe 62 into the part of the refrigerant pipe 2 communicating with the suction side of the compressor 4.

Since, thus, the gas refrigerant flows through the refrigerant inflow pipe 61 into the first buffer tank 63 and is then returned through the refrigerant return pipe 62 to the part of the refrigerant pipe 2 communicating with the suction side of the compressor 4, the gas refrigerant further smoothly flows through both the tanks 63, 64. This prevents the retention of gas refrigerant in the buffer tanks 63, 64 to provide circulation of all the refrigerant components of different specific gravities throughout the refrigerant circuit, which prevents the deterioration of the cooling capacity due to variations in the composition of the refrigerant mixture in the freezer R.

Embodiment 8

FIG. 13 shows the overall configuration of an ultra-low temperature freezer R according to Embodiment 8 of the invention. In this embodiment, the defrosting circuit 45 is configured to supply high-temperature gas refrigerant discharged from the compressor 4 to the fourth heat exchanger 21 as well as the cryocoil 32. Specifically, while the defrosting circuit 45 is connected at the upstream end to the refrigerant pipe 2 between the first oil separator 5 and the water-cooled condenser 8, the downstream end part of the defrosting circuit 45 is branched into a main branch circuit 45 a and a sub-branch circuit 45 b. The downstream end of the main branch circuit 45 a is connected to the main refrigerant pipe 2 a between the entrance of the cryocoil 32 and the sixth capillary tube 29. The downstream end of the sub-branch circuit 45 b is connected to the refrigerant pipe 2 between the exit of the cryocoil 32 and the secondary side of the fourth heat exchanger 21.

The solenoid shut-off valve 46 is connected into the defrosting circuit 45 upstream of the bifurcation of the main and sub-branch circuits 45 a, 45 b, and the solenoid shut-off valve 44 is connected into the main refrigerant pipe 2 a between the sixth capillary tube 29 and the cryocoil 32 and upstream of the connecting point with the downstream end of the main branch circuit 45 a (toward the sixth capillary tube 29). The rest of the configuration is the same as in Embodiment 4.

In this embodiment, during defrosting operation in which film deposition on substrates (wafers) is not carried out in the vacuum chamber 100 of the deposition apparatus A, the solenoid shut-off valve 46 is opened to open the defrosting circuit 45 and the solenoid shut-off valve 44 is closed to close the main refrigerant pipe 2 a. Thus, the high-temperature gas refrigerant discharged from the compressor 4 is supplied through the main branch circuit 45 a of the defrosting circuit 45 to the cryocoil 32 via its entrance and also supplied through the sub-branch circuit 45 b to the fourth heat exchanger 21 so that moisture or the like trapped in the cryocoil 32 and the fourth to second heat exchangers 21 to 19 is concurrently released.

As described above, the upstream end part of the defrosting circuit 45 is branched into the main branch circuit 45 a and the sub-branch circuit 45 b, the downstream end of the main branch circuit 45 a is connected to one side of the refrigerant pipe 2 toward the entrance of the cryocoil 32, and the downstream end of the sub-branch circuit 45 b is connected to the other side of the refrigerant pipe 2 toward the exit of the cryocoil 32. Therefore, the refrigerant flowing through the main branch circuit 45 a can be supplied to the cryocoil 32 to raise the temperature of the cryocoil 32 and, concurrently, the refrigerant flowing through the sub-branch circuit 45 b can be supplied to the fourth to second heat exchangers 21 to 19 connected to part of the refrigerant pipe 2 toward the exit of the cryocoil 32 to raise the temperatures of the fourth to second heat exchangers 21 to 19. Thus, it can be prevented that particularly at the start of defrosting operation, refrigerator oil or the like having passed through the cryocoil 32 still at an ultra-low temperature level is solidified again in the fourth to second heat exchangers 21 to 19. This ensures good circulation of the refrigerant mixture and provides shortened defrosting operation time, which in turn provides shortened time of exhaust from the vacuum chamber 100, shortened process time for film deposition and enhanced efficiency of film deposition.

Embodiment 9

FIG. 14 shows a refrigerant circuit of an ultra-low temperature freezer R according to Embodiment 9 of the invention. The difference of this embodiment from Embodiment 8 lies in that the sub-branch circuit 45 b of the defrosting circuit 45 is provided with a solenoid shut-off valve 68 connected partway therealong. The rest of the configuration is the same as in Embodiment 8.

In this embodiment, during defrosting operation in which film deposition on substrates is not carried out in the vacuum chamber 100 of the vacuum deposition apparatus A, the solenoid shut-off valve 68 is opened to open the sub-branch circuit 45 b and, likewise Embodiment 8, the solenoid shut-off valve 46 is opened to open the defrosting circuit 45 and the solenoid shut-off valve 44 is closed to close the main refrigerant pipe 2 a. Thus, the high-temperature gas refrigerant discharged from the compressor 4 is supplied through the main branch circuit 45 a of the defrosting circuit 45 to the cryocoil 32 and also supplied through the sub-branch circuit 45 b to the fourth heat exchanger 21 so that moisture or the like trapped in the cryocoil 32 and the fourth heat exchanger 21 is concurrently released.

Then, when the fourth heat exchanger 21 is raised in temperature up to the pour point (for example, −50° C.) of the refrigerator oil or higher, the solenoid shut-off valve 68 is closed to close the sub-branch circuit 45 b. Thus, the high-temperature gas refrigerant in the defrosting circuit 45, which has been distributed into the main branch circuit 45 a and the sub-branch circuit 45 b, flows only through the main branch circuit 45 a and is supplied to the cryocoil 32 to raise the temperature thereof. This provides further shortened defrosting operation time.

In this embodiment, the downstream end of the sub-branch circuit 45 b may not be connected to the secondary side of the fourth heat exchanger 21 but may be connected to the secondary side of any higher-temperature side heat exchanger. In other words, the downstream end of the sub-branch circuit 45 b may be connected to any portion of the refrigerant pipe 2 which reaches the pour point (for example, −50° C.) of the refrigerator oil or the like at which it smoothly flows or below the pour point, whereby high-temperature gas refrigerant (hot gas) can be supplied to that portion.

Embodiment 10

FIG. 15 shows Embodiment 10 of the invention, in which the configuration of the main refrigerant circuit 38 in the main refrigerant pipe 2 a is changed. Specifically, in this embodiment, the main refrigerant circuit 38 is branched partway therethrough into the first and second branch circuits 80, 81 connected in parallel with each other, and the main refrigerant circuit 38 is provided with the cryocoil 32 series-connected thereinto downstream of the bifurcation of the downstream ends of both the branch circuits 80, 81.

The first branch circuit 80 is provided with a first branch capillary tube 80 a series-connected thereinto. The second branch circuit 81 is provided with a solenoid shut-off valve 81 b and a second branch capillary tube 81 a which are series-connected into the second branch circuit 81 in order from upstream to downstream side. The solenoid shut-off valve 81 b constitutes a switch for turning the second branch circuit 81 on to supply the refrigerant thereto. Further, used as the first and second branch capillary tubes 80 a and 81 a are those having different pressure reduction capabilities. Though not shown, the ultra-low temperature freezer R is provided with a temperature sensor for detecting the temperature of the cryocoil 32. The rest of the configuration is the same as in Embodiment 4.

In this embodiment, during normal operation of the ultra-low temperature freezer R, the solenoid shut-off valve 46 is closed to close the defrosting circuit 45 and the solenoid shut-off valve 44 is opened to open the main refrigerant circuit 38. Further, the solenoid shut-off valve 81 b is opened to open the second branch circuit 81. Thus, out of gas-liquid mixture refrigerant having been discharged from the primary side of the fourth heat exchanger 21 and then having passed through the primary side of the supercooler 31, refrigerant flowing through the main refrigerant circuit 38 is distributed into two flows and then reduced in pressure by the first and second branch capillary tubes 80 a, 81 a. The refrigerant flows reduced in pressure then evaporate in the cryocoil 32 to apply a cold environment to moisture in the vacuum chamber 100.

In this case, since the solenoid shut-off valve 81 b is opened to distribute the refrigerant into the first and second branch circuits 80 and 81 and reduce the pressures of distributed flows by the first and second branch capillary tubes 80 a and 81 a, respectively, this increases the flow rate of refrigerant.

Then, when the detected value of the temperature sensor in the ultra-low temperature freezer R reaches a predetermined temperature (for example, −100° C. or below), the solenoid shut-off valve 81 b is closed so that the refrigerant flows only through the first branch capillary tube 80 a.

Consequently, this embodiment shortens the cooling time taken for the cooling target to reach an ultra-low temperature level while ensuring the cooling capacity to cool the cooling target down to the ultra-low temperature level by increasing the flow resistance of refrigerant, and in turn provides shortened process time for film deposition and enhanced efficiency of film deposition in the vacuum chamber 100.

Further, since the first and second branch capillary tubes 80 a, 81 a are used as pressure reducing elements, this ensures that refrigerant is reduced in pressure even in an ultra-low temperature range and provides higher reliability than when expansion valves or the like are used as pressure reducing elements, which is advantageous for stable operation of the freezer. Furthermore, since capillary tubes are lower in price than expansion valves, the equipment cost can be significantly reduced.

Though this embodiment employs capillary tubes having different pressure reduction capabilities as the first and second branch capillary tubes 80 a and 81 a, respectively, this invention may employ capillary tubes having the same pressure reduction capability as the first and second branch capillary tubes.

Embodiment 11

FIG. 16 shows a refrigerant circuit of an ultra-low temperature freezer R according to Embodiment 11 of the invention. The difference of this embodiment from Embodiment 8 lies just in the circuit configuration for capillary tubes connected between the primary side of the supercooler 31 and the entrance of the cryocoil 32.

Specifically, in this embodiment, the main refrigerant circuit 38 is formed partway therethrough with four branch circuits 80 to 83, from first to fourth, connected in parallel with each other. The cryocoil 32 is series-connected into the main refrigerant circuit 38 downstream of the confluence of the branch circuits 80 to 83.

Further, the first branch circuit 80 is provided with a first branch capillary tube 80 a series-connected thereinto. The second branch circuit 81 is provided with a solenoid shut-off valve 81 b and a second branch capillary tube 81 a which are arranged in order from upstream to downstream and series-connected into the second branch circuit 81. The third branch circuit 82 is provided with a solenoid shut-off valve 82 b and a third branch capillary tube 82 a which are arranged in order from upstream to downstream and series-connected into the third branch circuit 82. The fourth branch circuit 83 is provided with a solenoid shut-off valve 83 b and a fourth branch capillary tube 83 a which are arranged in order from upstream to downstream and series-connected into the fourth branch circuit 83. In this case, used as the first to fourth branch capillary tubes 80 a to 83 a are those having different pressure reduction capabilities. The rest of the configuration is the same as in Embodiment 10.

In this embodiment, during the operation of the ultra-low temperature freezer R when films are deposited on substrates in the vacuum chamber 100 of the vacuum deposition apparatus A, the gas-liquid mixture refrigerant, which flows through the main refrigerant circuit 38 after discharged from the primary side of the supercooler 31, is reduced in pressure by the first branch capillary tube 80 a of the first branch circuit 80. Further, in order to cool the cooling target in a short time, the solenoid shut-off valves 81 b to 83 b of the second to fourth branch circuit 81 to 83 are appropriately selectively opened. Thus, the gas-liquid mixture refrigerant is selectively distributed into and reduced in pressure by the second to fourth branch capillary tubes 81 a to 83 a. After reduced in pressure, the gas-liquid mixture refrigerant evaporates in the cryocoil 32 to apply a cold environment to moisture in the vacuum chamber 100.

Then, when the detected value of the temperature sensor reaches a predetermined temperature (for example, −100° C. or below), the solenoid shut-off valves 81 b to 83 b, for example, are closed to allow the refrigerant to flow only through the first branch capillary tube 80 a.

According to this embodiment, the solenoid shut-off valves 81 b to 83 b of the second to fourth branch circuits 81 to 83 can be selectively opened to distribute the refrigerant selectively into the second to fourth branch capillary tubes 81 a to 83 a. This enables flexible control on the cooling temperature in the vacuum chamber 100 and the cooling time taken until the cooling temperature is reached.

Though this embodiment has a circuit configuration in which the main refrigerant circuit 38 is divided into four branch circuits, i.e., first to fourth branch circuits 80 to 83, the present invention is not limited to this and may have, for example, a circuit configuration in which the main refrigerant circuit 38 is divided into three branch circuits or a circuit configuration in which it is divided into five or more branch circuits (see the imaginary lines in FIG. 16). This point also applies to the Embodiment 13 described later.

Embodiment 12

FIG. 17 shows a refrigerant circuit of an ultra-low temperature freezer R according to Embodiment 12 of the invention. The difference of this embodiment from Embodiment 10 lies just in the circuit configuration for capillary tubes connected between the supercooler 31 and the cryocoil 32.

Specifically, the main refrigerant circuit 38 is formed partway therethrough with first and second branch circuits 80, 81 connected in parallel with each other. The cryocoil 32 is series-connected into the main refrigerant circuit 38 downstream of the confluence of both the branch circuits 80, 81.

The first branch circuit 80 is provided with a first branch capillary tube 80 a and a solenoid shut-off valve 80 b which are arranged in order from upstream to downstream and series-connected into the first branch circuit 80. The second branch circuit 81 is provided with a second branch capillary tube 81 a and a solenoid shut-off valve 81 b which are arranged in order from upstream to downstream and series-connected into the second branch circuit 81. Used as the first and second branch capillary tubes 80 a, 81 a are those having different pressure reduction capabilities. Further, because during defrosting operation the main refrigerant circuit 38 is closed by simultaneously closing the solenoid shut-off valves 80 b, 81 b of the first and second branch circuits 80, 81, the solenoid shut-off valve 44 in Embodiment 10 (see FIG. 15) is not disposed here. The rest of the configuration is the same as in Embodiment 10.

In this embodiment, during the operation of the ultra-low temperature freezer R when films are deposited on substrates in the vacuum chamber 100 of the vacuum deposition apparatus A, the rest of the gas-liquid mixture refrigerant, which flows through the main refrigerant circuit 38 after discharged from the primary side of the supercooler 31, is distributed into and reduced in pressure by the first and second branch capillary tubes 80 a, 81 a through the opening of the solenoid shut-off valves 80 b, 81 b of the first and second branch circuits 80, 81. After reduced in pressure, the gas-liquid mixture refrigerant evaporates in the cryocoil 32 to apply a cold environment to moisture in the vacuum chamber 100.

Then, when the detected value of the temperature sensor or the pressure sensor reaches a predetermined temperature (for example, −100° C. or below) or a predetermined pressure, one of the solenoid shut-off valves 80 b, 81 b of the first and second branch circuits 80, 81 is closed to allow the refrigerant to flow only through the first or second branch capillary tube 80 a, 81 a.

According to this embodiment, the solenoid shut-off valves 80 b, 81 b of the first and second branch circuits 80, 81 can be selectively opened to selectively distribute the refrigerant into the first and second branch capillary tubes 80 a, 81 a. This enables flexible control on the cooling temperature in the vacuum chamber 100 and the cooling time taken until the cooling temperature is reached.

Instead of simultaneous opening of the two solenoid shut-off valves 80 b, 81 b, only one of them may be opened.

Embodiment 13

FIG. 18 shows a refrigerant circuit of an ultra-low temperature freezer R according to Embodiment 13. The difference of this embodiment from Embodiment 12 lies just in the circuit configuration for capillary tubes connected between the supercooler 31 and the cryocoil 32.

Specifically, in this embodiment, the main refrigerant circuit 38 is formed partway therethrough with first to fourth branch circuits 80 to 83 connected in parallel with each other. The cryocoil 32 is series-connected into the main refrigerant circuit 38 downstream of the confluence of the first to fourth branch circuits 80 to 83.

Further, the first branch circuit 80 is provided with a first branch capillary tube 80 a and a solenoid shut-off valve 80 b which are arranged in order from upstream to downstream and series-connected in the first branch circuit 80. The second branch circuit 81 is provided with a second branch capillary tube 81 a and a solenoid shut-off valve 81 b which are arranged in order from upstream to downstream and series-connected into the second branch circuit 81. The third branch circuit 82 is provided with a third branch capillary tube 82 a and a solenoid shut-off valve 82 b which are arranged in order from upstream to downstream and series-connected into the third branch circuit 82. The fourth branch circuit 83 is provided with a fourth branch capillary tube 83 a and a solenoid shut-off valve 83 b which are arranged in order from upstream to downstream and series-connected into the fourth branch circuit 83. Used as the first to fourth branch capillary tubes 80 a to 83 a are those having different pressure reduction capabilities. The rest of the configuration is the same as in Embodiment 12.

In this embodiment, during the operation of the ultra-low temperature freezer R when films are deposited on substrates in the vacuum chamber 100 of the vacuum deposition apparatus A, the solenoid shut-off valves 80 b to 83 b of the first to fourth branch circuit 80 to 83 are appropriately selectively opened in order to cool the cooling target in a short time. Thus, the rest of the gas-liquid mixture refrigerant, which flows through the main refrigerant circuit 38 after discharged from the primary side of the supercooler 31, is selectively distributed into and reduced in pressure by the first to fourth branch capillary tubes 80 a to 83 a. After reduced in pressure, the gas-liquid mixture refrigerant evaporates in the cryocoil 32 to apply a cold environment to moisture in the vacuum chamber 100.

Then, when the detected value of the temperature sensor reaches a predetermined temperature (for example, −100° C. or below), the solenoid shut-off valves 80 b to 83 b of the first to fourth branch circuits 80 to 83 are appropriately closed to pass the refrigerant selectively through the first to fourth branch capillary tubes 80 a to 83 a.

According to this embodiment, the solenoid shut-off valves 80 b to 83 b of the first to fourth branch circuits 80 to 83 can be selectively opened to distribute refrigerant selectively into the first to fourth branch capillary tubes 80 a to 83 a. This enables flexible control on the cooling temperature in the vacuum chamber 100 and the cooling time taken until the cooling temperature is reached.

Other Embodiments

In the above embodiments, the cryocoil 32 is disposed in the vacuum chamber 100 so that it directly cools moisture in the vacuum chamber 100. However, the present invention may be configured so that a brine cooler (exoergic part) is provided instead of the cryocoil 32 and connected through a brine circuit to an endoergic part located in the vacuum chamber 100, the brine in the brine circuit is cooled down to an ultra-low temperature level by the brine cooler and the cooled brine applies a cold environment at the same temperature level to the endoergic part in the vacuum chamber 100.

Further, the condensers 8, 10, heat exchangers 18 to 21 and supercooler 31 used may be of any one of double-pipe design, plate design and shell and tube design. Furthermore, instead of capillary tubes 24 to 29, other pressure reducing elements, such as expansion valves, may be used.

The above embodiments employ non-azeotropic refrigerant mixture obtained by mixing five or six kinds of refrigerants, for example. However, the present invention of course can be applied to refrigeration systems using other refrigerant mixtures obtained by mixing refrigerants of any number of kinds other than five or six. Further, though the above embodiments are used to cool moisture in the vacuum chamber 100 of the vacuum deposition apparatus A, the present invention may be applied to any refrigeration systems for cooling other cooling targets.

Furthermore, though the above embodiments employ a system in which gas-liquid separation is carried out in four stages, the present invention can be applied instead to any systems in which gas-liquid separation is carried out in three or less stages or five or more stages.

Furthermore, though the above embodiments employ a water-cooled system using the water-cooled condenser 21, the present invention may be configured instead into any systems using air-cooled condensers.

INDUSTRIAL APPLICABILITY

The present invention can obtain various highly practical effects, such as the ability to stably cool the cooling target even in the case of load variations, the ability to quickly cool the cooling target from normal to ultra-low temperature level to shorten the cool-down time, the ability to enhance the cooling efficiency while ensuring good circulation of refrigerant mixture during defrosting of an ultra-low temperature freezer with a defrosting circuit, the ability to smoothly circulate gas refrigerant in a buffer tank of the ultra-low temperature freezer into the refrigerant circuit to prevent the retention of gas refrigerant in the tank and thereby keep a good composition of the refrigerant, the ability to shorten the defrosting operation time and the ability to ensure a required cooling capacity for cooling the cooling target down to a predetermined cooling temperature and concurrently shorten the cooling time taken until the cooling target reaches the cooling temperature. Therefore, the present invention is very useful and has high industrial applicability. 

1. A refrigeration system comprising: a compressor for compressing refrigerant; a condenser for cooling the refrigerant discharged from the compressor to condense the refrigerant; a supercooler, having a primary side through which the refrigerant discharged from the condenser flows and a secondary side through which the refrigerant discharged from the primary side and reduced in pressure by a supercooler pressure reducing element flows, for cooling the refrigerant in the primary side by heat exchange with the refrigerant in the secondary side; a main cooler for evaporating the refrigerant discharged from the primary side of the supercooler and reduced in pressure by a main cooler pressure reducing element to cool a cooling target; and a supercooler refrigerant flow rate increasing device for allowing liquid refrigerant of the refrigerant discharged from the primary side of the supercooler to flow into the secondary side of the supercooler at a higher rate than into the main cooler.
 2. A refrigeration system comprising: a compressor for compressing refrigerant mixture in which plural kinds of refrigerants having different boiling points are mixed; a condenser for cooling a high-boiling refrigerant component in the refrigerant mixture discharged from the compressor to condense the high-boiling refrigerant component; multiple stages of gas-liquid separators for separating individual refrigerant components in the refrigerant mixture discharged from the condenser into liquid refrigerant and gas refrigerant in order from higher- to lower-boiling refrigerant components; multiple stages of cascade heat exchangers for individually cooling the gas refrigerant separated by the associated gas-liquid separator by heat exchange with the liquid refrigerant separated by the associated gas-liquid separator and then reduced in pressure by a pressure reducing element; a supercooler, having a primary side through which the low-boiling refrigerant component discharged from the final-stage cascade heat exchanger flows and a secondary side through which the low-boiling refrigerant component discharged from the primary side and reduced in pressure by a supercooler pressure reducing element flows, for cooling the low-boiling refrigerant component in the primary side by heat exchange with the low-boiling refrigerant component in the secondary side; a main cooler for evaporating the low-boiling refrigerant component discharged from the primary side of the supercooler and reduced in pressure by a main cooler pressure reducing element to cool a cooling target down to an ultra-low temperature level; and a supercooler refrigerant flow rate increasing device for allowing liquid refrigerant of the refrigerant discharged from the primary side of the supercooler to flow into the secondary side of the supercooler at a higher rate than into the main cooler.
 3. The refrigeration system of claim 1 or 2, wherein the refrigeration system further comprises: a main refrigerant circuit provided with the main cooler and the main cooler pressure reducing element; and a sub refrigerant circuit that is connected at the upstream end to the upstream end of the main refrigerant circuit to branch off therefrom and provided with the supercooler pressure reducing element, and the supercooler refrigerant flow rate increasing device is configured so that the minimum cross sectional area of the sub refrigerant circuit is larger than the maximum cross sectional area of the main refrigerant circuit.
 4. The refrigeration system of claim 1 or 2, wherein the refrigeration system further comprises: a main refrigerant circuit provided with the main cooler and the main cooler pressure reducing element; and a sub refrigerant circuit that is connected at the upstream end to the upstream end of the main refrigerant circuit to branch off therefrom and provided with the supercooler pressure reducing element, and the supercooler refrigerant flow rate increasing device is configured so that the maximum height of the sub refrigerant circuit at the bifurcation of the main and sub refrigerant circuits is lower than the minimum height of the main refrigerant circuit at the bifurcation.
 5. The refrigeration system of claim 3, wherein the supercooler refrigerant flow rate increasing device is configured so that the maximum height of the sub refrigerant circuit at the bifurcation of the main and sub refrigerant circuits is lower than the minimum height of the main refrigerant circuit at the bifurcation.
 6. A vacuum apparatus configured to freeze moisture in a vacuum chamber by cooling the moisture through the main cooler in the refrigeration system of any one of claims 1 to
 2. 7. An ultra-low temperature freezer comprising: a compressor for compressing refrigerant mixture in which plural kinds of refrigerants having different boiling points are mixed; a condenser for cooling a high-boiling refrigerant component in the refrigerant mixture discharged from the compressor to liquefy the high-boiling refrigerant component; a first oil separator for removing, from the refrigerant mixture flowing from the discharge side of the compressor toward the condenser, refrigerator oil mixed in the refrigerant mixture; multiple stages of gas-liquid separators for separating individual refrigerant components in the refrigerant mixture liquefied by the condenser into liquid refrigerant and gas refrigerant in order from higher- to lower-boiling refrigerant components; multiple stages of cascade heat exchangers for individually cooling the gas refrigerant separated by the associated gas-liquid separator by heat exchange with the liquid refrigerant separated by the associated gas-liquid separator and reduced in pressure; a cooler for evaporating the low-boiling refrigerant component discharged from the final-stage cascade heat exchanger of the multiple stages of cascade heat exchangers and reduced in pressure to cool a cooling target down to an ultra-low temperature level; and a defrosting circuit for supplying the refrigerant mixture discharged from the compressor to the cooler during defrosting of the cooler, wherein the defrosting circuit is provided with a second oil separator for removing refrigerator oil from the refrigerant mixture.
 8. The ultra-low temperature freezer of claim 7, wherein the defrosting circuit is provided with a shut-off valve that is opened during defrosting, and the second oil separator is disposed between the upstream end of the defrosting circuit and the shut-off valve.
 9. The ultra-low temperature freezer of claim 7 or 8, wherein the second oil separator is disposed at a location along the defrosting circuit at which the distance to the upstream end of the defrosting circuit is shorter than the distance to the downstream end thereof.
 10. An ultra-low temperature freezer comprising a refrigerant circuit in which are connected: a compressor for compressing refrigerant mixture in which plural kinds of refrigerants having different boiling points are mixed; a condenser for cooling a high-boiling refrigerant component in the refrigerant mixture discharged from the compressor to liquefy the high-boiling refrigerant component; multiple stages of gas-liquid separators for separating individual refrigerant components in the refrigerant mixture liquefied by the condenser into liquid refrigerant and gas refrigerant in order from higher- to lower-boiling refrigerant components; multiple stages of cascade heat exchangers for individually cooling the gas refrigerant separated by the associated gas-liquid separator by heat exchange with the liquid refrigerant separated by the associated gas-liquid separator and reduced in pressure; and a cooler for evaporating the low-boiling refrigerant component discharged from the final-stage cascade heat exchanger of the multiple stages of cascade heat exchangers and reduced in pressure to cool a cooling target down to an ultra-low temperature level, wherein the refrigerant circuit is connected with a plurality of buffer tanks for restraining abnormal increase in the discharge pressure of the compressor.
 11. The ultra-low temperature freezer of claim 10, wherein the plurality of buffer tanks include at least one first buffer tank and at least one second buffer tank located below the first buffer tank, the first and second buffer tanks are connected to each other through a communicating passage for providing flow communication of gas refrigerant between the first and second buffer tanks, and the second buffer tank is connected to one side of the refrigerant circuit toward the discharge part of the compressor and the other side toward the suction part of the compressor.
 12. The ultra-low temperature freezer of claim 10, wherein the plurality of buffer tanks include at least one first buffer tank and at least one second buffer tank, the first and second buffer tanks are connected to each other through a communicating passage for providing flow communication of gas refrigerant between the first and second buffer tanks, the first buffer tank is connected to the side of the refrigerant circuit located toward the discharge part of the compressor, and the communicating passage is connected partway therethrough to the side of the refrigerant circuit located toward the suction part of the compressor.
 13. The ultra-low temperature freezer of claim 10, wherein the plurality of buffer tanks include at least one first buffer tank and at least one second buffer tank, the first and second buffer tanks are connected to each other through a communicating passage for providing flow communication of gas refrigerant between the first and second buffer tanks, the first buffer tank is connected to the side of the refrigerant circuit located toward the discharge part of the compressor, and the second buffer tank is connected to the side of the refrigerant circuit located toward the suction part of the compressor.
 14. An ultra-low temperature freezer comprising a refrigerant circuit in which are connected: a compressor for compressing refrigerant mixture in which plural kinds of refrigerants having different boiling points are mixed; a condenser for cooling a high-boiling refrigerant component in the refrigerant mixture discharged from the compressor to liquefy the high-boiling refrigerant component; multiple stages of gas-liquid separators for separating individual refrigerant components in the refrigerant mixture liquefied by the condenser into liquid refrigerant and gas refrigerant in order from higher- to lower-boiling refrigerant components; multiple stages of cascade heat exchangers for individually cooling the gas refrigerant separated by the associated gas-liquid separator by heat exchange with the liquid refrigerant separated by the associated gas-liquid separator and reduced in pressure; and a cooler for evaporating the low-boiling refrigerant component discharged from the final-stage cascade heat exchanger of the multiple stages of cascade heat exchangers and reduced in pressure to cool a cooling target down to an ultra-low temperature level, and a defrosting circuit for supplying the refrigerant mixture discharged from the compressor to the cooler during defrosting of the cooler, wherein the downstream end part of the defrosting circuit is branched into a main branch circuit and a sub-branch circuit, the downstream end of the main branch circuit is connected to one side of the refrigerant circuit toward the entrance of the cooler, and the downstream end of the sub-branch circuit is connected to the other side of the refrigerant circuit toward the exit of the cooler.
 15. The ultra-low temperature freezer of claim 14, wherein the sub-branch circuit is provided with a shut-off valve.
 16. An ultra-low temperature freezer comprising a refrigerant circuit in which are connected: a compressor for compressing refrigerant mixture in which plural kinds of refrigerants having different boiling points are mixed; a condenser for cooling a high-boiling refrigerant component in the refrigerant mixture discharged from the compressor to liquefy the high-boiling refrigerant component; multiple stages of gas-liquid separators for separating individual refrigerant components in the refrigerant mixture liquefied by the condenser into liquid refrigerant and gas refrigerant in order from higher- to lower-boiling refrigerant components; multiple stages of cascade heat exchangers for individually cooling the gas refrigerant separated by the associated gas-liquid separator by heat exchange with the liquid refrigerant separated by the associated gas-liquid separator and reduced in pressure; a pressure reducing element for reducing the pressure of the low-boiling refrigerant component discharged from the final-stage cascade heat exchanger of the multiple stages of cascade heat exchangers; and a cooler for evaporating the low-boiling refrigerant component reduced in pressure by the pressure reducing element to cool a cooling target down to an ultra-low temperature level, wherein part of the refrigerant circuit for supplying refrigerant from the final-stage cascade heat exchanger to the cooler comprises a plurality of branch circuits connected in parallel with each other, the pressure reducing element comprises a plurality of branch pressure reducing elements series-connected into the plurality of branch circuits, respectively, and at least one of the plurality of branch circuits is provided with a selector for turning the at least one branch circuit on to pass the refrigerant therethrough.
 17. The ultra-low temperature freezer of claim 16, wherein the selector comprises a shut-off valve disposed in at least one of the plurality of branch circuits.
 18. The ultra-low temperature freezer of claim 16 or 17, wherein the plurality of branch pressure reducing elements have different pressure reduction capabilities.
 19. The ultra-low temperature freezer of any one of claims 16 or 17, wherein the branch pressure reducing element comprises a capillary tube.
 20. A vacuum apparatus configured to freeze moisture in a vacuum chamber by cooling the moisture with the cooler in the ultra-low temperature freezer of any one of claims 7, 10 and
 14. 